Ticket #41750: 41750.2.diff

src/wp-includes/class-phpmailer.php

@@ -1 +1 @@
 <?php
 /**
  * PHPMailer - PHP email creation and transport class.
- * PHP Version 5
- * @package PHPMailer
- * @link https://github.com/PHPMailer/PHPMailer/ The PHPMailer GitHub project
- * @author Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
- * @author Jim Jagielski (jimjag) <jimjag@gmail.com>
- * @author Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
- * @author Brent R. Matzelle (original founder)
- * @copyright 2012 - 2014 Marcus Bointon
+ * PHP Version 5.5.
+ *
+ * @see       https://github.com/PHPMailer/PHPMailer/ The PHPMailer GitHub project
+ *
+ * @author    Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
+ * @author    Jim Jagielski (jimjag) <jimjag@gmail.com>
+ * @author    Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
+ * @author    Brent R. Matzelle (original founder)
+ * @copyright 2012 - 2017 Marcus Bointon
  * @copyright 2010 - 2012 Jim Jagielski
  * @copyright 2004 - 2009 Andy Prevost
- * @license http://www.gnu.org/copyleft/lesser.html GNU Lesser General Public License
- * @note This program is distributed in the hope that it will be useful - WITHOUT
+ * @license   http://www.gnu.org/copyleft/lesser.html GNU Lesser General Public License
+ * @note      This program is distributed in the hope that it will be useful - WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.
  */
 
+namespace PHPMailer\PHPMailer;
+
 /**
  * PHPMailer - PHP email creation and transport class.
- * @package PHPMailer
- * @author Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
- * @author Jim Jagielski (jimjag) <jimjag@gmail.com>
- * @author Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
- * @author Brent R. Matzelle (original founder)
+ *
+ * @author  Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
+ * @author  Jim Jagielski (jimjag) <jimjag@gmail.com>
+ * @author  Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
+ * @author  Brent R. Matzelle (original founder)
  */
 class PHPMailer
 {
-    /**
-     * The PHPMailer Version number.
-     * @var string
-     */
-    public $Version = '5.2.27';
+    const CHARSET_ISO88591 = 'iso-8859-1';
+    const CHARSET_UTF8 = 'utf-8';
+
+    const CONTENT_TYPE_PLAINTEXT = 'text/plain';
+    const CONTENT_TYPE_TEXT_CALENDAR = 'text/calendar';
+    const CONTENT_TYPE_TEXT_HTML = 'text/html';
+    const CONTENT_TYPE_MULTIPART_ALTERNATIVE = 'multipart/alternative';
+    const CONTENT_TYPE_MULTIPART_MIXED = 'multipart/mixed';
+    const CONTENT_TYPE_MULTIPART_RELATED = 'multipart/related';
+
+    const ENCODING_7BIT = '7bit';
+    const ENCODING_8BIT = '8bit';
+    const ENCODING_BASE64 = 'base64';
+    const ENCODING_BINARY = 'binary';
+    const ENCODING_QUOTED_PRINTABLE = 'quoted-printable';
 
     /**
      * Email priority.
      * Options: null (default), 1 = High, 3 = Normal, 5 = low.
      * When null, the header is not set at all.
-     * @var integer
+     *
+     * @var int
      */
-    public $Priority = null;
+    public $Priority;
 
     /**
      * The character set of the message.
+     *
      * @var string
      */
-    public $CharSet = 'iso-8859-1';
+    public $CharSet = self::CHARSET_ISO88591;
 
     /**
      * The MIME Content-type of the message.
+     *
      * @var string
      */
-    public $ContentType = 'text/plain';
+    public $ContentType = self::CONTENT_TYPE_PLAINTEXT;
 
     /**
      * The message encoding.
      * Options: "8bit", "7bit", "binary", "base64", and "quoted-printable".
+     *
      * @var string
      */
-    public $Encoding = '8bit';
+    public $Encoding = self::ENCODING_8BIT;
 
     /**
      * Holds the most recent mailer error message.
+     *
      * @var string
      */
     public $ErrorInfo = '';
 
     /**
      * The From email address for the message.
+     *
      * @var string
      */
     public $From = 'root@localhost';
 
     /**
      * The From name of the message.
+     *
      * @var string
      */
     public $FromName = 'Root User';
 
     /**
-     * The Sender email (Return-Path) of the message.
-     * If not empty, will be sent via -f to sendmail or as 'MAIL FROM' in smtp mode.
+     * The envelope sender of the message.
+     * This will usually be turned into a Return-Path header by the receiver,
+     * and is the address that bounces will be sent to.
+     * If not empty, will be passed via `-f` to sendmail or as the 'MAIL FROM' value over SMTP.
+     *
      * @var string
      */
     public $Sender = '';
 
     /**
-     * The Return-Path of the message.
-     * If empty, it will be set to either From or Sender.
-     * @var string
-     * @deprecated Email senders should never set a return-path header;
-     * it's the receiver's job (RFC5321 section 4.4), so this no longer does anything.
-     * @link https://tools.ietf.org/html/rfc5321#section-4.4 RFC5321 reference
-     */
-    public $ReturnPath = '';
-
-    /**
      * The Subject of the message.
+     *
      * @var string
      */
     public $Subject = '';
@@ -104 +118 @@
     /**
      * An HTML or plain text message body.
      * If HTML then call isHTML(true).
+     *
      * @var string
      */
     public $Body = '';
@@ -113 +128 @@
      * This body can be read by mail clients that do not have HTML email
      * capability such as mutt & Eudora.
      * Clients that can read HTML will view the normal Body.
+     *
      * @var string
      */
     public $AltBody = '';
@@ -120 +136 @@
     /**
      * An iCal message part body.
      * Only supported in simple alt or alt_inline message types
-     * To generate iCal events, use the bundled extras/EasyPeasyICS.php class or iCalcreator
-     * @link http://sprain.ch/blog/downloads/php-class-easypeasyics-create-ical-files-with-php/
-     * @link http://kigkonsult.se/iCalcreator/
+     * To generate iCal event structures, use classes like EasyPeasyICS or iCalcreator.
+     *
+     * @see http://sprain.ch/blog/downloads/php-class-easypeasyics-create-ical-files-with-php/
+     * @see http://kigkonsult.se/iCalcreator/
+     *
      * @var string
      */
     public $Ical = '';
 
     /**
      * The complete compiled MIME message body.
-     * @access protected
+     *
      * @var string
      */
     protected $MIMEBody = '';
 
     /**
      * The complete compiled MIME message headers.
+     *
      * @var string
-     * @access protected
      */
     protected $MIMEHeader = '';
 
     /**
      * Extra headers that createHeader() doesn't fold in.
+     *
      * @var string
-     * @access protected
      */
     protected $mailHeader = '';
 
     /**
      * Word-wrap the message body to this number of chars.
      * Set to 0 to not wrap. A useful value here is 78, for RFC2822 section 2.1.1 compliance.
-     * @var integer
+     *
+     * @see static::STD_LINE_LENGTH
+     *
+     * @var int
      */
     public $WordWrap = 0;
 
     /**
      * Which method to use to send mail.
      * Options: "mail", "sendmail", or "smtp".
+     *
      * @var string
      */
     public $Mailer = 'mail';
 
     /**
      * The path to the sendmail program.
+     *
      * @var string
      */
     public $Sendmail = '/usr/sbin/sendmail';
@@ -171 +194 @@
     /**
      * Whether mail() uses a fully sendmail-compatible MTA.
      * One which supports sendmail's "-oi -f" options.
-     * @var boolean
+     *
+     * @var bool
      */
     public $UseSendmailOptions = true;
 
     /**
-     * Path to PHPMailer plugins.
-     * Useful if the SMTP class is not in the PHP include path.
-     * @var string
-     * @deprecated Should not be needed now there is an autoloader.
-     */
-    public $PluginDir = '';
-
-    /**
      * The email address that a reading confirmation should be sent to, also known as read receipt.
+     *
      * @var string
      */
     public $ConfirmReadingTo = '';
@@ -194 +211 @@
      * If empty, PHPMailer attempts to find one with, in order,
      * $_SERVER['SERVER_NAME'], gethostname(), php_uname('n'), or the value
      * 'localhost.localdomain'.
+     *
      * @var string
      */
     public $Hostname = '';
@@ -203 +221 @@
      * If empty, a unique id will be generated.
      * You can set your own, but it must be in the format "<id@domain>",
      * as defined in RFC5322 section 3.6.4 or it will be ignored.
+     *
      * @see https://tools.ietf.org/html/rfc5322#section-3.6.4
+     *
      * @var string
      */
     public $MessageID = '';
@@ -211 +231 @@
     /**
      * The message Date to be used in the Date header.
      * If empty, the current date will be added.
+     *
      * @var string
      */
     public $MessageDate = '';
@@ -224 +245 @@
      * You can also specify encryption type, for example:
      * (e.g. "tls://smtp1.example.com:587;ssl://smtp2.example.com:465").
      * Hosts will be tried in order.
+     *
      * @var string
      */
     public $Host = 'localhost';
 
     /**
      * The default SMTP server port.
-     * @var integer
-     * @TODO Why is this needed when the SMTP class takes care of it?
+     *
+     * @var int
      */
     public $Port = 25;
 
@@ -239 +261 @@
      * The SMTP HELO of the message.
      * Default is $Hostname. If $Hostname is empty, PHPMailer attempts to find
      * one with the same method described above for $Hostname.
-     * @var string
+     *
      * @see PHPMailer::$Hostname
+     *
+     * @var string
      */
     public $Helo = '';
 
     /**
      * What kind of encryption to use on the SMTP connection.
-     * Options: '', 'ssl' or 'tls'
+     * Options: '', 'ssl' or 'tls'.
+     *
      * @var string
      */
     public $SMTPSecure = '';
@@ -255 +280 @@
      * Whether to enable TLS encryption automatically if a server supports it,
      * even if `SMTPSecure` is not set to 'tls'.
      * Be aware that in PHP >= 5.6 this requires that the server's certificates are valid.
-     * @var boolean
+     *
+     * @var bool
      */
     public $SMTPAutoTLS = true;
 
     /**
      * Whether to use SMTP authentication.
      * Uses the Username and Password properties.
-     * @var boolean
+     *
      * @see PHPMailer::$Username
      * @see PHPMailer::$Password
+     *
+     * @var bool
      */
     public $SMTPAuth = false;
 
     /**
      * Options array passed to stream_context_create when connecting via SMTP.
+     *
      * @var array
      */
-    public $SMTPOptions = array();
+    public $SMTPOptions = [];
 
     /**
      * SMTP username.
+     *
      * @var string
      */
     public $Username = '';
 
     /**
      * SMTP password.
+     *
      * @var string
      */
     public $Password = '';
 
     /**
      * SMTP auth type.
-     * Options are CRAM-MD5, LOGIN, PLAIN, attempted in that order if not specified
+     * Options are CRAM-MD5, LOGIN, PLAIN, XOAUTH2, attempted in that order if not specified.
+     *
      * @var string
      */
     public $AuthType = '';
 
     /**
-     * SMTP realm.
-     * Used for NTLM auth
-     * @var string
-     */
-    public $Realm = '';
-
-    /**
-     * SMTP workstation.
-     * Used for NTLM auth
-     * @var string
+     * An instance of the PHPMailer OAuth class.
+     *
+     * @var OAuth
      */
-    public $Workstation = '';
+    protected $oauth;
 
     /**
      * The SMTP server timeout in seconds.
-     * Default of 5 minutes (300sec) is from RFC2821 section 4.5.3.2
-     * @var integer
+     * Default of 5 minutes (300sec) is from RFC2821 section 4.5.3.2.
+     *
+     * @var int
      */
     public $Timeout = 300;
 
@@ -322 +348 @@
      * * `1` Commands
      * * `2` Data and commands
      * * `3` As 2 plus connection status
-     * * `4` Low-level data output
-     * @var integer
+     * * `4` Low-level data output.
+     *
      * @see SMTP::$do_debug
+     *
+     * @var int
      */
     public $SMTPDebug = 0;
 
@@ -334 +362 @@
      * * `echo` Output plain-text as-is, appropriate for CLI
      * * `html` Output escaped, line breaks converted to `<br>`, appropriate for browser output
      * * `error_log` Output to error log as configured in php.ini
-     *
+     * By default PHPMailer will use `echo` if run from a `cli` or `cli-server` SAPI, `html` otherwise.
      * Alternatively, you can provide a callable expecting two params: a message string and the debug level:
-     * <code>
+     *
+     * ```php
      * $mail->Debugoutput = function($str, $level) {echo "debug level $level; message: $str";};
-     * </code>
-     * @var string|callable
+     * ```
+     *
+     * Alternatively, you can pass in an instance of a PSR-3 compatible logger, though only `debug`
+     * level output is used:
+     *
+     * ```php
+     * $mail->Debugoutput = new myPsr3Logger;
+     * ```
+     *
      * @see SMTP::$Debugoutput
+     *
+     * @var string|callable|\Psr\Log\LoggerInterface
      */
     public $Debugoutput = 'echo';
 
@@ -348 +386 @@
      * Whether to keep SMTP connection open after each message.
      * If this is set to true then to close the connection
      * requires an explicit call to smtpClose().
-     * @var boolean
+     *
+     * @var bool
      */
     public $SMTPKeepAlive = false;
 
@@ -356 +395 @@
      * Whether to split multiple to addresses into multiple messages
      * or send them all in one message.
      * Only supported in `mail` and `sendmail` transports, not in SMTP.
-     * @var boolean
+     *
+     * @var bool
      */
     public $SingleTo = false;
 
     /**
      * Storage for addresses when SingleTo is enabled.
+     *
      * @var array
-     * @TODO This should really not be public
      */
-    public $SingleToArray = array();
+    protected $SingleToArray = [];
 
     /**
      * Whether to generate VERP addresses on send.
      * Only applicable when sending via SMTP.
-     * @link https://en.wikipedia.org/wiki/Variable_envelope_return_path
-     * @link http://www.postfix.org/VERP_README.html Postfix VERP info
-     * @var boolean
+     *
+     * @see https://en.wikipedia.org/wiki/Variable_envelope_return_path
+     * @see http://www.postfix.org/VERP_README.html Postfix VERP info
+     *
+     * @var bool
      */
     public $do_verp = false;
 
     /**
      * Whether to allow sending messages with an empty body.
-     * @var boolean
+     *
+     * @var bool
      */
     public $AllowEmpty = false;
 
     /**
-     * The default line ending.
-     * @note The default remains "\n". We force CRLF where we know
-     *        it must be used via self::CRLF.
-     * @var string
-     */
-    public $LE = "\n";
-
-    /**
      * DKIM selector.
+     *
      * @var string
      */
     public $DKIM_selector = '';
@@ -399 +435 @@
     /**
      * DKIM Identity.
      * Usually the email address used as the source of the email.
+     *
      * @var string
      */
     public $DKIM_identity = '';
@@ -406 +443 @@
     /**
      * DKIM passphrase.
      * Used if your key is encrypted.
+     *
      * @var string
      */
     public $DKIM_passphrase = '';
 
     /**
      * DKIM signing domain name.
+     *
      * @example 'example.com'
+     *
      * @var string
      */
     public $DKIM_domain = '';
 
     /**
+     * DKIM Copy header field values for diagnostic use.
+     *
+     * @var bool
+     */
+    public $DKIM_copyHeaderFields = true;
+
+    /**
+     * DKIM Extra signing headers.
+     *
+     * @example ['List-Unsubscribe', 'List-Help']
+     *
+     * @var array
+     */
+    public $DKIM_extraHeaders = [];
+
+    /**
      * DKIM private key file path.
+     *
      * @var string
      */
     public $DKIM_private = '';
 
     /**
      * DKIM private key string.
+     *
      * If set, takes precedence over `$DKIM_private`.
+     *
      * @var string
      */
     public $DKIM_private_string = '';
@@ -439 +498 @@
      * Value can be any php callable: http://www.php.net/is_callable
      *
      * Parameters:
-     *   boolean $result        result of the send action
+     *   bool $result        result of the send action
      *   array   $to            email addresses of the recipients
      *   array   $cc            cc email addresses
      *   array   $bcc           bcc email addresses
      *   string  $subject       the subject
      *   string  $body          the email body
      *   string  $from          email address of sender
+     *   string  $extra         extra information of possible use
+     *                          "smtp_transaction_id' => last smtp transaction id
+     *
      * @var string
      */
     public $action_function = '';
 
     /**
      * What to put in the X-Mailer header.
-     * Options: An empty string for PHPMailer default, whitespace for none, or a string to use
+     * Options: An empty string for PHPMailer default, whitespace for none, or a string to use.
+     *
      * @var string
      */
     public $XMailer = '';
@@ -460 +523 @@
     /**
      * Which validator to use by default when validating email addresses.
      * May be a callable to inject your own validator, but there are several built-in validators.
+     * The default validator uses PHP's FILTER_VALIDATE_EMAIL filter_var option.
+     *
      * @see PHPMailer::validateAddress()
+     *
      * @var string|callable
-     * @static
      */
-    public static $validator = 'auto';
+    public static $validator = 'php';
 
     /**
      * An instance of the SMTP sender class.
+     *
      * @var SMTP
-     * @access protected
      */
-    protected $smtp = null;
+    protected $smtp;
 
     /**
      * The array of 'to' names and addresses.
+     *
      * @var array
-     * @access protected
      */
-    protected $to = array();
+    protected $to = [];
 
     /**
      * The array of 'cc' names and addresses.
+     *
      * @var array
-     * @access protected
      */
-    protected $cc = array();
+    protected $cc = [];
 
     /**
      * The array of 'bcc' names and addresses.
+     *
      * @var array
-     * @access protected
      */
-    protected $bcc = array();
+    protected $bcc = [];
 
     /**
      * The array of reply-to names and addresses.
+     *
      * @var array
-     * @access protected
      */
-    protected $ReplyTo = array();
+    protected $ReplyTo = [];
 
     /**
      * An array of all kinds of addresses.
-     * Includes all of $to, $cc, $bcc
+     * Includes all of $to, $cc, $bcc.
+     *
+     * @see PHPMailer::$to
+     * @see PHPMailer::$cc
+     * @see PHPMailer::$bcc
+     *
      * @var array
-     * @access protected
-     * @see PHPMailer::$to @see PHPMailer::$cc @see PHPMailer::$bcc
      */
-    protected $all_recipients = array();
+    protected $all_recipients = [];
 
     /**
      * An array of names and addresses queued for validation.
      * In send(), valid and non duplicate entries are moved to $all_recipients
      * and one of $to, $cc, or $bcc.
      * This array is used only for addresses with IDN.
-     * @var array
-     * @access protected
-     * @see PHPMailer::$to @see PHPMailer::$cc @see PHPMailer::$bcc
+     *
+     * @see PHPMailer::$to
+     * @see PHPMailer::$cc
+     * @see PHPMailer::$bcc
      * @see PHPMailer::$all_recipients
+     *
+     * @var array
      */
-    protected $RecipientsQueue = array();
+    protected $RecipientsQueue = [];
 
     /**
      * An array of reply-to names and addresses queued for validation.
      * In send(), valid and non duplicate entries are moved to $ReplyTo.
      * This array is used only for addresses with IDN.
-     * @var array
-     * @access protected
+     *
      * @see PHPMailer::$ReplyTo
+     *
+     * @var array
      */
-    protected $ReplyToQueue = array();
+    protected $ReplyToQueue = [];
 
     /**
      * The array of attachments.
+     *
      * @var array
-     * @access protected
      */
-    protected $attachment = array();
+    protected $attachment = [];
 
     /**
      * The array of custom headers.
+     *
      * @var array
-     * @access protected
      */
-    protected $CustomHeader = array();
+    protected $CustomHeader = [];
 
     /**
      * The most recent Message-ID (including angular brackets).
+     *
      * @var string
-     * @access protected
      */
     protected $lastMessageID = '';
 
     /**
      * The message's MIME type.
+     *
      * @var string
-     * @access protected
      */
     protected $message_type = '';
 
     /**
      * The array of MIME boundary strings.
+     *
      * @var array
-     * @access protected
      */
-    protected $boundary = array();
+    protected $boundary = [];
 
     /**
      * The array of available languages.
+     *
      * @var array
-     * @access protected
      */
-    protected $language = array();
+    protected $language = [];
 
     /**
      * The number of errors encountered.
-     * @var integer
-     * @access protected
+     *
+     * @var int
      */
     protected $error_count = 0;
 
     /**
      * The S/MIME certificate file path.
+     *
      * @var string
-     * @access protected
      */
     protected $sign_cert_file = '';
 
     /**
      * The S/MIME key file path.
+     *
      * @var string
-     * @access protected
      */
     protected $sign_key_file = '';
 
     /**
      * The optional S/MIME extra certificates ("CA Chain") file path.
+     *
      * @var string
-     * @access protected
      */
     protected $sign_extracerts_file = '';
 
     /**
      * The S/MIME password for the key.
      * Used only if the key is encrypted.
+     *
      * @var string
-     * @access protected
      */
     protected $sign_key_pass = '';
 
     /**
      * Whether to throw exceptions for errors.
-     * @var boolean
-     * @access protected
+     *
+     * @var bool
      */
     protected $exceptions = false;
 
     /**
      * Unique ID used for message ID and boundaries.
+     *
      * @var string
-     * @access protected
      */
     protected $uniqueid = '';
 
     /**
+     * The PHPMailer Version number.
+     *
+     * @var string
+     */
+    const VERSION = '6.0.7';
+
+    /**
      * Error severity: message only, continue processing.
+     *
+     * @var int
      */
     const STOP_MESSAGE = 0;
 
     /**
      * Error severity: message, likely ok to continue processing.
+     *
+     * @var int
      */
     const STOP_CONTINUE = 1;
 
     /**
      * Error severity: message, plus full stop, critical error reached.
+     *
+     * @var int
      */
     const STOP_CRITICAL = 2;
 
     /**
      * SMTP RFC standard line ending.
+     *
+     * @var string
      */
-    const CRLF = "\r\n";
+    protected static $LE = "\r\n";
 
     /**
-     * The maximum line length allowed by RFC 2822 section 2.1.1
-     * @var integer
+     * The maximum line length allowed by RFC 2822 section 2.1.1.
+     *
+     * @var int
      */
     const MAX_LINE_LENGTH = 998;
 
     /**
+     * The lower maximum line length allowed by RFC 2822 section 2.1.1.
+     * This length does NOT include the line break
+     * 76 means that lines will be 77 or 78 chars depending on whether
+     * the line break format is LF or CRLF; both are valid.
+     *
+     * @var int
+     */
+    const STD_LINE_LENGTH = 76;
+
+    /**
      * Constructor.
-     * @param boolean $exceptions Should we throw external exceptions?
+     *
+     * @param bool $exceptions Should we throw external exceptions?
      */
     public function __construct($exceptions = null)
     {
-        if ($exceptions !== null) {
-            $this->exceptions = (boolean)$exceptions;
+        if (null !== $exceptions) {
+            $this->exceptions = (bool) $exceptions;
         }
         //Pick an appropriate debug output format automatically
         $this->Debugoutput = (strpos(PHP_SAPI, 'cli') !== false ? 'echo' : 'html');
@@ -676 +775 @@
      * Call mail() in a safe_mode-aware fashion.
      * Also, unless sendmail_path points to sendmail (or something that
      * claims to be sendmail), don't pass params (not a perfect fix,
-     * but it will do)
-     * @param string $to To
-     * @param string $subject Subject
-     * @param string $body Message Body
-     * @param string $header Additional Header(s)
-     * @param string $params Params
-     * @access private
-     * @return boolean
+     * but it will do).
+     *
+     * @param string      $to      To
+     * @param string      $subject Subject
+     * @param string      $body    Message Body
+     * @param string      $header  Additional Header(s)
+     * @param string|null $params  Params
+     *
+     * @return bool
      */
     private function mailPassthru($to, $subject, $body, $header, $params)
     {
@@ -693 +793 @@
         } else {
             $subject = $this->encodeHeader($this->secureHeader($subject));
         }
-
-        //Can't use additional_parameters in safe_mode, calling mail() with null params breaks
-        //@link http://php.net/manual/en/function.mail.php
-        if (ini_get('safe_mode') or !$this->UseSendmailOptions or is_null($params)) {
+        //Calling mail() with null params breaks
+        if (!$this->UseSendmailOptions or null === $params) {
             $result = @mail($to, $subject, $body, $header);
         } else {
             $result = @mail($to, $subject, $body, $header, $params);
         }
+
         return $result;
     }
+
     /**
      * Output debugging info via user-defined method.
      * Only generates output if SMTP debug output is enabled (@see SMTP::$do_debug).
+     *
      * @see PHPMailer::$Debugoutput
      * @see PHPMailer::$SMTPDebug
+     *
      * @param string $str
      */
     protected function edebug($str)
@@ -715 +817 @@
         if ($this->SMTPDebug <= 0) {
             return;
         }
+        //Is this a PSR-3 logger?
+        if ($this->Debugoutput instanceof \Psr\Log\LoggerInterface) {
+            $this->Debugoutput->debug($str);
+
+            return;
+        }
         //Avoid clash with built-in function names
-        if (!in_array($this->Debugoutput, array('error_log', 'html', 'echo')) and is_callable($this->Debugoutput)) {
+        if (!in_array($this->Debugoutput, ['error_log', 'html', 'echo']) and is_callable($this->Debugoutput)) {
             call_user_func($this->Debugoutput, $str, $this->SMTPDebug);
+
             return;
         }
         switch ($this->Debugoutput) {
@@ -731 +840 @@
                     preg_replace('/[\r\n]+/', '', $str),
                     ENT_QUOTES,
                     'UTF-8'
-                )
-                . "<br>\n";
+                ), "<br>\n";
                 break;
             case 'echo':
             default:
                 //Normalize line breaks
-                $str = preg_replace('/\r\n?/ms', "\n", $str);
-                echo gmdate('Y-m-d H:i:s') . "\t" . str_replace(
-                    "\n",
-                    "\n                   \t                  ",
-                    trim($str)
-                ) . "\n";
+                $str = preg_replace('/\r\n|\r/ms', "\n", $str);
+                echo gmdate('Y-m-d H:i:s'),
+                "\t",
+                    //Trim trailing space
+                trim(
+                //Indent for readability, except for trailing break
+                    str_replace(
+                        "\n",
+                        "\n                   \t                  ",
+                        trim($str)
+                    )
+                ),
+                "\n";
         }
     }
 
     /**
      * Sets message type to HTML or plain.
-     * @param boolean $isHtml True for HTML mode.
-     * @return void
+     *
+     * @param bool $isHtml True for HTML mode
      */
     public function isHTML($isHtml = true)
     {
         if ($isHtml) {
-            $this->ContentType = 'text/html';
+            $this->ContentType = static::CONTENT_TYPE_TEXT_HTML;
         } else {
-            $this->ContentType = 'text/plain';
+            $this->ContentType = static::CONTENT_TYPE_PLAINTEXT;
         }
     }
 
     /**
      * Send messages using SMTP.
-     * @return void
      */
     public function isSMTP()
     {
@@ -771 +885 @@
 
     /**
      * Send messages using PHP's mail() function.
-     * @return void
      */
     public function isMail()
     {
@@ -780 +893 @@
 
     /**
      * Send messages using $Sendmail.
-     * @return void
      */
     public function isSendmail()
     {
         $ini_sendmail_path = ini_get('sendmail_path');
 
-        if (!stristr($ini_sendmail_path, 'sendmail')) {
+        if (false === stripos($ini_sendmail_path, 'sendmail')) {
             $this->Sendmail = '/usr/sbin/sendmail';
         } else {
             $this->Sendmail = $ini_sendmail_path;
@@ -796 +908 @@
 
     /**
      * Send messages using qmail.
-     * @return void
      */
     public function isQmail()
     {
         $ini_sendmail_path = ini_get('sendmail_path');
 
-        if (!stristr($ini_sendmail_path, 'qmail')) {
+        if (false === stripos($ini_sendmail_path, 'qmail')) {
             $this->Sendmail = '/var/qmail/bin/qmail-inject';
         } else {
             $this->Sendmail = $ini_sendmail_path;
@@ -812 +923 @@
 
     /**
      * Add a "To" address.
+     *
      * @param string $address The email address to send to
      * @param string $name
-     * @return boolean true on success, false if address already used or invalid in some way
+     *
+     * @return bool true on success, false if address already used or invalid in some way
      */
     public function addAddress($address, $name = '')
     {
@@ -823 +936 @@
 
     /**
      * Add a "CC" address.
-     * @note: This function works with the SMTP mailer on win32, not with the "mail" mailer.
+     *
      * @param string $address The email address to send to
      * @param string $name
-     * @return boolean true on success, false if address already used or invalid in some way
+     *
+     * @return bool true on success, false if address already used or invalid in some way
      */
     public function addCC($address, $name = '')
     {
@@ -835 +949 @@
 
     /**
      * Add a "BCC" address.
-     * @note: This function works with the SMTP mailer on win32, not with the "mail" mailer.
+     *
      * @param string $address The email address to send to
      * @param string $name
-     * @return boolean true on success, false if address already used or invalid in some way
+     *
+     * @return bool true on success, false if address already used or invalid in some way
      */
     public function addBCC($address, $name = '')
     {
@@ -847 +962 @@
 
     /**
      * Add a "Reply-To" address.
+     *
      * @param string $address The email address to reply to
      * @param string $name
-     * @return boolean true on success, false if address already used or invalid in some way
+     *
+     * @return bool true on success, false if address already used or invalid in some way
      */
     public function addReplyTo($address, $name = '')
     {
@@ -861 +978 @@
      * can't validate addresses with an IDN without knowing the PHPMailer::$CharSet (that can still
      * be modified after calling this function), addition of such addresses is delayed until send().
      * Addresses that have been added already return false, but do not throw exceptions.
-     * @param string $kind One of 'to', 'cc', 'bcc', or 'ReplyTo'
+     *
+     * @param string $kind    One of 'to', 'cc', 'bcc', or 'ReplyTo'
      * @param string $address The email address to send, resp. to reply to
      * @param string $name
-     * @throws phpmailerException
-     * @return boolean true on success, false if address already used or invalid in some way
-     * @access protected
+     *
+     * @throws \Exception
+     *
+     * @return bool true on success, false if address already used or invalid in some way
      */
     protected function addOrEnqueueAnAddress($kind, $address, $name)
     {
         $address = trim($address);
         $name = trim(preg_replace('/[\r\n]+/', '', $name)); //Strip breaks and trim
-        if (($pos = strrpos($address, '@')) === false) {
-            // At-sign is misssing.
-            $error_message = $this->lang('invalid_address') . " (addAnAddress $kind): $address";
+        $pos = strrpos($address, '@');
+        if (false === $pos) {
+            // At-sign is missing.
+            $error_message = sprintf('%s (%s): %s',
+                $this->lang('invalid_address'),
+                $kind,
+                $address);
             $this->setError($error_message);
             $this->edebug($error_message);
             if ($this->exceptions) {
-                throw new phpmailerException($error_message);
+                throw new \Exception($error_message);
             }
+
             return false;
         }
-        $params = array($kind, $address, $name);
+        $params = [$kind, $address, $name];
         // Enqueue addresses with IDN until we know the PHPMailer::$CharSet.
-        if ($this->has8bitChars(substr($address, ++$pos)) and $this->idnSupported()) {
-            if ($kind != 'Reply-To') {
+        if ($this->has8bitChars(substr($address, ++$pos)) and static::idnSupported()) {
+            if ('Reply-To' != $kind) {
                 if (!array_key_exists($address, $this->RecipientsQueue)) {
                     $this->RecipientsQueue[$address] = $params;
+
                     return true;
                 }
             } else {
                 if (!array_key_exists($address, $this->ReplyToQueue)) {
                     $this->ReplyToQueue[$address] = $params;
+
                     return true;
                 }
             }
+
             return false;
         }
+
         // Immediately add standard addresses without IDN.
-        return call_user_func_array(array($this, 'addAnAddress'), $params);
+        return call_user_func_array([$this, 'addAnAddress'], $params);
     }
 
     /**
      * Add an address to one of the recipient arrays or to the ReplyTo array.
      * Addresses that have been added already return false, but do not throw exceptions.
-     * @param string $kind One of 'to', 'cc', 'bcc', or 'ReplyTo'
+     *
+     * @param string $kind    One of 'to', 'cc', 'bcc', or 'ReplyTo'
      * @param string $address The email address to send, resp. to reply to
      * @param string $name
-     * @throws phpmailerException
-     * @return boolean true on success, false if address already used or invalid in some way
-     * @access protected
+     *
+     * @throws \Exception
+     *
+     * @return bool true on success, false if address already used or invalid in some way
      */
     protected function addAnAddress($kind, $address, $name = '')
     {
-        if (!in_array($kind, array('to', 'cc', 'bcc', 'Reply-To'))) {
-            $error_message = $this->lang('Invalid recipient kind: ') . $kind;
+        if (!in_array($kind, ['to', 'cc', 'bcc', 'Reply-To'])) {
+            $error_message = sprintf('%s: %s',
+                $this->lang('Invalid recipient kind'),
+                $kind);
             $this->setError($error_message);
             $this->edebug($error_message);
             if ($this->exceptions) {
-                throw new phpmailerException($error_message);
+                throw new \Exception($error_message);
             }
+
             return false;
         }
-        if (!$this->validateAddress($address)) {
-            $error_message = $this->lang('invalid_address') . " (addAnAddress $kind): $address";
+        if (!static::validateAddress($address)) {
+            $error_message = sprintf('%s (%s): %s',
+                $this->lang('invalid_address'),
+                $kind,
+                $address);
             $this->setError($error_message);
             $this->edebug($error_message);
             if ($this->exceptions) {
-                throw new phpmailerException($error_message);
+                throw new \Exception($error_message);
             }
+
             return false;
         }
-        if ($kind != 'Reply-To') {
+        if ('Reply-To' != $kind) {
             if (!array_key_exists(strtolower($address), $this->all_recipients)) {
-                array_push($this->$kind, array($address, $name));
+                $this->{$kind}[] = [$address, $name];
                 $this->all_recipients[strtolower($address)] = true;
+
                 return true;
             }
         } else {
             if (!array_key_exists(strtolower($address), $this->ReplyTo)) {
-                $this->ReplyTo[strtolower($address)] = array($address, $name);
+                $this->ReplyTo[strtolower($address)] = [$address, $name];
+
                 return true;
             }
         }
+
         return false;
     }
 
@@ -952 +1092 @@
      * of the form "display name <address>" into an array of name/address pairs.
      * Uses the imap_rfc822_parse_adrlist function if the IMAP extension is available.
      * Note that quotes in the name part are removed.
+     *
+     * @see    http://www.andrew.cmu.edu/user/agreen1/testing/mrbs/web/Mail/RFC822.php A more careful implementation
+     *
      * @param string $addrstr The address list string
-     * @param bool $useimap Whether to use the IMAP extension to parse the list
+     * @param bool   $useimap Whether to use the IMAP extension to parse the list
+     *
      * @return array
-     * @link http://www.andrew.cmu.edu/user/agreen1/testing/mrbs/web/Mail/RFC822.php A more careful implementation
      */
-    public function parseAddresses($addrstr, $useimap = true)
+    public static function parseAddresses($addrstr, $useimap = true)
     {
-        $addresses = array();
+        $addresses = [];
         if ($useimap and function_exists('imap_rfc822_parse_adrlist')) {
             //Use this built-in parser if it's available
             $list = imap_rfc822_parse_adrlist($addrstr, '');
             foreach ($list as $address) {
-                if ($address->host != '.SYNTAX-ERROR.') {
-                    if ($this->validateAddress($address->mailbox . '@' . $address->host)) {
-                        $addresses[] = array(
+                if ('.SYNTAX-ERROR.' != $address->host) {
+                    if (static::validateAddress($address->mailbox . '@' . $address->host)) {
+                        $addresses[] = [
                             'name' => (property_exists($address, 'personal') ? $address->personal : ''),
-                            'address' => $address->mailbox . '@' . $address->host
-                        );
+                            'address' => $address->mailbox . '@' . $address->host,
+                        ];
                     }
                 }
             }
@@ -981 +1124 @@
                 //Is there a separate name part?
                 if (strpos($address, '<') === false) {
                     //No separate name, just use the whole thing
-                    if ($this->validateAddress($address)) {
-                        $addresses[] = array(
+                    if (static::validateAddress($address)) {
+                        $addresses[] = [
                             'name' => '',
-                            'address' => $address
-                        );
+                            'address' => $address,
+                        ];
                     }
                 } else {
                     list($name, $email) = explode('<', $address);
                     $email = trim(str_replace('>', '', $email));
-                    if ($this->validateAddress($email)) {
-                        $addresses[] = array(
-                            'name' => trim(str_replace(array('"', "'"), '', $name)),
-                            'address' => $email
-                        );
+                    if (static::validateAddress($email)) {
+                        $addresses[] = [
+                            'name' => trim(str_replace(['"', "'"], '', $name)),
+                            'address' => $email,
+                        ];
                     }
                 }
             }
         }
+
         return $addresses;
     }
 
     /**
      * Set the From and FromName properties.
+     *
      * @param string $address
      * @param string $name
-     * @param boolean $auto Whether to also set the Sender address, defaults to true
-     * @throws phpmailerException
-     * @return boolean
+     * @param bool   $auto    Whether to also set the Sender address, defaults to true
+     *
+     * @throws \Exception
+     *
+     * @return bool
      */
     public function setFrom($address, $name = '', $auto = true)
     {
         $address = trim($address);
         $name = trim(preg_replace('/[\r\n]+/', '', $name)); //Strip breaks and trim
         // Don't validate now addresses with IDN. Will be done in send().
-        if (($pos = strrpos($address, '@')) === false or
-            (!$this->has8bitChars(substr($address, ++$pos)) or !$this->idnSupported()) and
-            !$this->validateAddress($address)) {
-            $error_message = $this->lang('invalid_address') . " (setFrom) $address";
+        $pos = strrpos($address, '@');
+        if (false === $pos or
+            (!$this->has8bitChars(substr($address, ++$pos)) or !static::idnSupported()) and
+            !static::validateAddress($address)) {
+            $error_message = sprintf('%s (From): %s',
+                $this->lang('invalid_address'),
+                $address);
             $this->setError($error_message);
             $this->edebug($error_message);
             if ($this->exceptions) {
-                throw new phpmailerException($error_message);
+                throw new \Exception($error_message);
             }
+
             return false;
         }
         $this->From = $address;
@@ -1033 +1184 @@
                 $this->Sender = $address;
             }
         }
+
         return true;
     }
 
@@ -1041 +1193 @@
      * Technically this is the value from the last time the headers were created,
      * but it's also the message ID of the last sent message except in
      * pathological cases.
+     *
      * @return string
      */
     public function getLastMessageID()
@@ -1050 +1203 @@
 
     /**
      * Check that a string looks like an email address.
-     * @param string $address The email address to check
-     * @param string|callable $patternselect A selector for the validation pattern to use :
+     * Validation patterns supported:
      * * `auto` Pick best pattern automatically;
-     * * `pcre8` Use the squiloople.com pattern, requires PCRE > 8.0, PHP >= 5.3.2, 5.2.14;
+     * * `pcre8` Use the squiloople.com pattern, requires PCRE > 8.0;
      * * `pcre` Use old PCRE implementation;
      * * `php` Use PHP built-in FILTER_VALIDATE_EMAIL;
      * * `html5` Use the pattern given by the HTML5 spec for 'email' type form input elements.
      * * `noregex` Don't use a regex: super fast, really dumb.
      * Alternatively you may pass in a callable to inject your own validator, for example:
+     *
+     * ```php
      * PHPMailer::validateAddress('user@example.com', function($address) {
      *     return (strpos($address, '@') !== false);
      * });
+     * ```
+     *
      * You can also set the PHPMailer::$validator static to a callable, allowing built-in methods to use your validator.
-     * @return boolean
-     * @static
-     * @access public
+     *
+     * @param string          $address       The email address to check
+     * @param string|callable $patternselect Which pattern to use
+     *
+     * @return bool
      */
     public static function validateAddress($address, $patternselect = null)
     {
-        if (is_null($patternselect)) {
-            $patternselect = self::$validator;
+        if (null === $patternselect) {
+            $patternselect = static::$validator;
         }
         if (is_callable($patternselect)) {
             return call_user_func($patternselect, $address);
@@ -1079 +1237 @@
         if (strpos($address, "\n") !== false or strpos($address, "\r") !== false) {
             return false;
         }
-        if (!$patternselect or $patternselect == 'auto') {
-            //Check this constant first so it works when extension_loaded() is disabled by safe mode
-            //Constant was added in PHP 5.2.4
-            if (defined('PCRE_VERSION')) {
-                //This pattern can get stuck in a recursive loop in PCRE <= 8.0.2
-                if (version_compare(PCRE_VERSION, '8.0.3') >= 0) {
-                    $patternselect = 'pcre8';
-                } else {
-                    $patternselect = 'pcre';
-                }
-            } elseif (function_exists('extension_loaded') and extension_loaded('pcre')) {
-                //Fall back to older PCRE
-                $patternselect = 'pcre';
-            } else {
-                //Filter_var appeared in PHP 5.2.0 and does not require the PCRE extension
-                if (version_compare(PHP_VERSION, '5.2.0') >= 0) {
-                    $patternselect = 'php';
-                } else {
-                    $patternselect = 'noregex';
-                }
-            }
-        }
         switch ($patternselect) {
+            case 'pcre': //Kept for BC
             case 'pcre8':
-                /**
-                 * Uses the same RFC5322 regex on which FILTER_VALIDATE_EMAIL is based, but allows dotless domains.
-                 * @link http://squiloople.com/2009/12/20/email-address-validation/
+                /*
+                 * A more complex and more permissive version of the RFC5322 regex on which FILTER_VALIDATE_EMAIL
+                 * is based.
+                 * In addition to the addresses allowed by filter_var, also permits:
+                 *  * dotless domains: `a@b`
+                 *  * comments: `1234 @ local(blah) .machine .example`
+                 *  * quoted elements: `'"test blah"@example.org'`
+                 *  * numeric TLDs: `a@b.123`
+                 *  * unbracketed IPv4 literals: `a@192.168.0.1`
+                 *  * IPv6 literals: 'first.last@[IPv6:a1::]'
+                 * Not all of these will necessarily work for sending!
+                 *
+                 * @see       http://squiloople.com/2009/12/20/email-address-validation/
                  * @copyright 2009-2010 Michael Rushton
                  * Feel free to use and redistribute this code. But please keep this copyright notice.
                  */
-                return (boolean)preg_match(
+                return (bool) preg_match(
                     '/^(?!(?>(?1)"?(?>\\\[ -~]|[^"])"?(?1)){255,})(?!(?>(?1)"?(?>\\\[ -~]|[^"])"?(?1)){65,}@)' .
                     '((?>(?>(?>((?>(?>(?>\x0D\x0A)?[\t ])+|(?>[\t ]*\x0D\x0A)?[\t ]+)?)(\((?>(?2)' .
                     '(?>[\x01-\x08\x0B\x0C\x0E-\'*-\[\]-\x7F]|\\\[\x00-\x7F]|(?3)))*(?2)\)))+(?2))|(?2))?)' .
@@ -1121 +1268 @@
                     '|[1-9]?[0-9])(?>\.(?9)){3}))\])(?1)$/isD',
                     $address
                 );
-            case 'pcre':
-                //An older regex that doesn't need a recent PCRE
-                return (boolean)preg_match(
-                    '/^(?!(?>"?(?>\\\[ -~]|[^"])"?){255,})(?!(?>"?(?>\\\[ -~]|[^"])"?){65,}@)(?>' .
-                    '[!#-\'*+\/-9=?^-~-]+|"(?>(?>[\x01-\x08\x0B\x0C\x0E-!#-\[\]-\x7F]|\\\[\x00-\xFF]))*")' .
-                    '(?>\.(?>[!#-\'*+\/-9=?^-~-]+|"(?>(?>[\x01-\x08\x0B\x0C\x0E-!#-\[\]-\x7F]|\\\[\x00-\xFF]))*"))*' .
-                    '@(?>(?![a-z0-9-]{64,})(?>[a-z0-9](?>[a-z0-9-]*[a-z0-9])?)(?>\.(?![a-z0-9-]{64,})' .
-                    '(?>[a-z0-9](?>[a-z0-9-]*[a-z0-9])?)){0,126}|\[(?:(?>IPv6:(?>(?>[a-f0-9]{1,4})(?>:' .
-                    '[a-f0-9]{1,4}){7}|(?!(?:.*[a-f0-9][:\]]){8,})(?>[a-f0-9]{1,4}(?>:[a-f0-9]{1,4}){0,6})?' .
-                    '::(?>[a-f0-9]{1,4}(?>:[a-f0-9]{1,4}){0,6})?))|(?>(?>IPv6:(?>[a-f0-9]{1,4}(?>:' .
-                    '[a-f0-9]{1,4}){5}:|(?!(?:.*[a-f0-9]:){6,})(?>[a-f0-9]{1,4}(?>:[a-f0-9]{1,4}){0,4})?' .
-                    '::(?>(?:[a-f0-9]{1,4}(?>:[a-f0-9]{1,4}){0,4}):)?))?(?>25[0-5]|2[0-4][0-9]|1[0-9]{2}' .
-                    '|[1-9]?[0-9])(?>\.(?>25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9]?[0-9])){3}))\])$/isD',
-                    $address
-                );
             case 'html5':
-                /**
+                /*
                  * This is the pattern used in the HTML5 spec for validation of 'email' type form input elements.
-                 * @link http://www.whatwg.org/specs/web-apps/current-work/#e-mail-state-(type=email)
+                 *
+                 * @see http://www.whatwg.org/specs/web-apps/current-work/#e-mail-state-(type=email)
                  */
-                return (boolean)preg_match(
+                return (bool) preg_match(
                     '/^[a-zA-Z0-9.!#$%&\'*+\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}' .
                     '[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/sD',
                     $address
                 );
-            case 'noregex':
-                //No PCRE! Do something _very_ approximate!
-                //Check the address is 3 chars or longer and contains an @ that's not the first or last char
-                return (strlen($address) >= 3
-                    and strpos($address, '@') >= 1
-                    and strpos($address, '@') != strlen($address) - 1);
             case 'php':
             default:
-                return (boolean)filter_var($address, FILTER_VALIDATE_EMAIL);
+                return (bool) filter_var($address, FILTER_VALIDATE_EMAIL);
         }
     }
 
     /**
      * Tells whether IDNs (Internationalized Domain Names) are supported or not. This requires the
-     * "intl" and "mbstring" PHP extensions.
-     * @return bool "true" if required functions for IDN support are present
+     * `intl` and `mbstring` PHP extensions.
+     *
+     * @return bool `true` if required functions for IDN support are present
      */
-    public function idnSupported()
+    public static function idnSupported()
     {
-        // @TODO: Write our own "idn_to_ascii" function for PHP <= 5.2.
         return function_exists('idn_to_ascii') and function_exists('mb_convert_encoding');
     }
 
@@ -1175 +1302 @@
      * This function silently returns unmodified address if:
      * - No conversion is necessary (i.e. domain name is not an IDN, or is already in ASCII form)
      * - Conversion to punycode is impossible (e.g. required PHP functions are not available)
-     *   or fails for any reason (e.g. domain has characters not allowed in an IDN)
-     * @see PHPMailer::$CharSet
+     *   or fails for any reason (e.g. domain contains characters not allowed in an IDN).
+     *
+     * @see    PHPMailer::$CharSet
+     *
      * @param string $address The email address to convert
+     *
      * @return string The encoded address in ASCII form
      */
     public function punyencodeAddress($address)
     {
         // Verify we have required functions, CharSet, and at-sign.
-        if ($this->idnSupported() and
+        $pos = strrpos($address, '@');
+        if (static::idnSupported() and
             !empty($this->CharSet) and
-            ($pos = strrpos($address, '@')) !== false) {
+            false !== $pos
+        ) {
             $domain = substr($address, ++$pos);
             // Verify CharSet string is a valid one, and domain properly encoded in this CharSet.
             if ($this->has8bitChars($domain) and @mb_check_encoding($domain, $this->CharSet)) {
                 $domain = mb_convert_encoding($domain, 'UTF-8', $this->CharSet);
-                if (($punycode = defined('INTL_IDNA_VARIANT_UTS46') ?
-                    idn_to_ascii($domain, 0, INTL_IDNA_VARIANT_UTS46) :
-                    idn_to_ascii($domain)) !== false) {
+                //Ignore IDE complaints about this line - method signature changed in PHP 5.4
+                $errorcode = 0;
+                $punycode = idn_to_ascii($domain, $errorcode, INTL_IDNA_VARIANT_UTS46);
+                if (false !== $punycode) {
                     return substr($address, 0, $pos) . $punycode;
                 }
             }
         }
+
         return $address;
     }
 
     /**
      * Create a message and send it.
      * Uses the sending method specified by $Mailer.
-     * @throws phpmailerException
-     * @return boolean false on error - See the ErrorInfo property for details of the error.
+     *
+     * @throws \Exception
+     *
+     * @return bool false on error - See the ErrorInfo property for details of the error
      */
     public function send()
     {
@@ -1212 +1348 @@
             if (!$this->preSend()) {
                 return false;
             }
+
             return $this->postSend();
-        } catch (phpmailerException $exc) {
+        } catch (\Exception $exc) {
             $this->mailHeader = '';
             $this->setError($exc->getMessage());
             if ($this->exceptions) {
                 throw $exc;
             }
+
             return false;
         }
     }
 
     /**
      * Prepare a message for sending.
-     * @throws phpmailerException
-     * @return boolean
+     *
+     * @throws \Exception
+     *
+     * @return bool
      */
     public function preSend()
     {
+        if ('smtp' == $this->Mailer or
+            ('mail' == $this->Mailer and stripos(PHP_OS, 'WIN') === 0)
+        ) {
+            //SMTP mandates RFC-compliant line endings
+            //and it's also used with mail() on Windows
+            static::setLE("\r\n");
+        } else {
+            //Maintain backward compatibility with legacy Linux command line mailers
+            static::setLE(PHP_EOL);
+        }
+        //Check for buggy PHP versions that add a header with an incorrect line break
+        if (ini_get('mail.add_x_header') == 1
+            and 'mail' == $this->Mailer
+            and stripos(PHP_OS, 'WIN') === 0
+            and ((version_compare(PHP_VERSION, '7.0.0', '>=')
+                    and version_compare(PHP_VERSION, '7.0.17', '<'))
+                or (version_compare(PHP_VERSION, '7.1.0', '>=')
+                    and version_compare(PHP_VERSION, '7.1.3', '<')))
+        ) {
+            trigger_error(
+                'Your version of PHP is affected by a bug that may result in corrupted messages.' .
+                ' To fix it, switch to sending using SMTP, disable the mail.add_x_header option in' .
+                ' your php.ini, switch to MacOS or Linux, or upgrade your PHP to version 7.0.17+ or 7.1.3+.',
+                E_USER_WARNING
+            );
+        }
+
         try {
             $this->error_count = 0; // Reset errors
             $this->mailHeader = '';
@@ -1237 +1404 @@
             // Dequeue recipient and Reply-To addresses with IDN
             foreach (array_merge($this->RecipientsQueue, $this->ReplyToQueue) as $params) {
                 $params[1] = $this->punyencodeAddress($params[1]);
-                call_user_func_array(array($this, 'addAnAddress'), $params);
+                call_user_func_array([$this, 'addAnAddress'], $params);
             }
-            if ((count($this->to) + count($this->cc) + count($this->bcc)) < 1) {
-                throw new phpmailerException($this->lang('provide_address'), self::STOP_CRITICAL);
+            if (count($this->to) + count($this->cc) + count($this->bcc) < 1) {
+                throw new \Exception($this->lang('provide_address'), self::STOP_CRITICAL);
             }
 
             // Validate From, Sender, and ConfirmReadingTo addresses
-            foreach (array('From', 'Sender', 'ConfirmReadingTo') as $address_kind) {
+            foreach (['From', 'Sender', 'ConfirmReadingTo'] as $address_kind) {
                 $this->$address_kind = trim($this->$address_kind);
                 if (empty($this->$address_kind)) {
                     continue;
                 }
                 $this->$address_kind = $this->punyencodeAddress($this->$address_kind);
-                if (!$this->validateAddress($this->$address_kind)) {
-                    $error_message = $this->lang('invalid_address') . ' (punyEncode) ' . $this->$address_kind;
+                if (!static::validateAddress($this->$address_kind)) {
+                    $error_message = sprintf('%s (%s): %s',
+                        $this->lang('invalid_address'),
+                        $address_kind,
+                        $this->$address_kind);
                     $this->setError($error_message);
                     $this->edebug($error_message);
                     if ($this->exceptions) {
-                        throw new phpmailerException($error_message);
+                        throw new \Exception($error_message);
                     }
+
                     return false;
                 }
             }
 
             // Set whether the message is multipart/alternative
             if ($this->alternativeExists()) {
-                $this->ContentType = 'multipart/alternative';
+                $this->ContentType = static::CONTENT_TYPE_MULTIPART_ALTERNATIVE;
             }
 
             $this->setMessageType();
             // Refuse to send an empty message unless we are specifically allowing it
             if (!$this->AllowEmpty and empty($this->Body)) {
-                throw new phpmailerException($this->lang('empty_message'), self::STOP_CRITICAL);
+                throw new \Exception($this->lang('empty_message'), self::STOP_CRITICAL);
             }
 
+            //Trim subject consistently
+            $this->Subject = trim($this->Subject);
             // Create body before headers in case body makes changes to headers (e.g. altering transfer encoding)
             $this->MIMEHeader = '';
             $this->MIMEBody = $this->createBody();
@@ -1282 +1455 @@
 
             // To capture the complete message when using mail(), create
             // an extra header list which createHeader() doesn't fold in
-            if ($this->Mailer == 'mail') {
+            if ('mail' == $this->Mailer) {
                 if (count($this->to) > 0) {
                     $this->mailHeader .= $this->addrAppend('To', $this->to);
                 } else {
@@ -1290 +1463 @@
                 }
                 $this->mailHeader .= $this->headerLine(
                     'Subject',
-                    $this->encodeHeader($this->secureHeader(trim($this->Subject)))
+                    $this->encodeHeader($this->secureHeader($this->Subject))
                 );
             }
 
@@ -1299 +1472 @@
                 and !empty($this->DKIM_selector)
                 and (!empty($this->DKIM_private_string)
                     or (!empty($this->DKIM_private)
-                        and self::isPermittedPath($this->DKIM_private)
+                        and static::isPermittedPath($this->DKIM_private)
                         and file_exists($this->DKIM_private)
                     )
                 )
@@ -1309 +1482 @@
                     $this->encodeHeader($this->secureHeader($this->Subject)),
                     $this->MIMEBody
                 );
-                $this->MIMEHeader = rtrim($this->MIMEHeader, "\r\n ") . self::CRLF .
-                    str_replace("\r\n", "\n", $header_dkim) . self::CRLF;
+                $this->MIMEHeader = rtrim($this->MIMEHeader, "\r\n ") . static::$LE .
+                    static::normalizeBreaks($header_dkim) . static::$LE;
             }
+
             return true;
-        } catch (phpmailerException $exc) {
+        } catch (\Exception $exc) {
             $this->setError($exc->getMessage());
             if ($this->exceptions) {
                 throw $exc;
             }
+
             return false;
         }
     }
 
     /**
-     * Actually send a message.
-     * Send the email via the selected mechanism
-     * @throws phpmailerException
-     * @return boolean
+     * Actually send a message via the selected mechanism.
+     *
+     * @throws \Exception
+     *
+     * @return bool
      */
     public function postSend()
     {
@@ -1341 +1517 @@
                 case 'mail':
                     return $this->mailSend($this->MIMEHeader, $this->MIMEBody);
                 default:
-                    $sendMethod = $this->Mailer.'Send';
+                    $sendMethod = $this->Mailer . 'Send';
                     if (method_exists($this, $sendMethod)) {
                         return $this->$sendMethod($this->MIMEHeader, $this->MIMEBody);
                     }
 
                     return $this->mailSend($this->MIMEHeader, $this->MIMEBody);
             }
-        } catch (phpmailerException $exc) {
+        } catch (\Exception $exc) {
             $this->setError($exc->getMessage());
             $this->edebug($exc->getMessage());
             if ($this->exceptions) {
                 throw $exc;
             }
         }
+
         return false;
     }
 
     /**
      * Send mail using the $Sendmail program.
+     *
+     * @see    PHPMailer::$Sendmail
+     *
      * @param string $header The message headers
-     * @param string $body The message body
-     * @see PHPMailer::$Sendmail
-     * @throws phpmailerException
-     * @access protected
-     * @return boolean
+     * @param string $body   The message body
+     *
+     * @throws \Exception
+     *
+     * @return bool
      */
     protected function sendmailSend($header, $body)
     {
         // CVE-2016-10033, CVE-2016-10045: Don't pass -f if characters will be escaped.
         if (!empty($this->Sender) and self::isShellSafe($this->Sender)) {
-            if ($this->Mailer == 'qmail') {
+            if ('qmail' == $this->Mailer) {
                 $sendmailFmt = '%s -f%s';
             } else {
                 $sendmailFmt = '%s -oi -f%s -t';
             }
         } else {
-            if ($this->Mailer == 'qmail') {
+            if ('qmail' == $this->Mailer) {
                 $sendmailFmt = '%s';
             } else {
                 $sendmailFmt = '%s -oi -t';
             }
         }
 
-        // TODO: If possible, this should be changed to escapeshellarg.  Needs thorough testing.
         $sendmail = sprintf($sendmailFmt, escapeshellcmd($this->Sendmail), $this->Sender);
 
         if ($this->SingleTo) {
             foreach ($this->SingleToArray as $toAddr) {
-                if (!@$mail = popen($sendmail, 'w')) {
-                    throw new phpmailerException($this->lang('execute') . $this->Sendmail, self::STOP_CRITICAL);
-                }
-                fputs($mail, 'To: ' . $toAddr . "\n");
-                fputs($mail, $header);
-                fputs($mail, $body);
+                $mail = @popen($sendmail, 'w');
+                if (!$mail) {
+                    throw new \Exception($this->lang('execute') . $this->Sendmail, self::STOP_CRITICAL);
+                }
+                fwrite($mail, 'To: ' . $toAddr . "\n");
+                fwrite($mail, $header);
+                fwrite($mail, $body);
                 $result = pclose($mail);
                 $this->doCallback(
                     ($result == 0),
-                    array($toAddr),
+                    [$toAddr],
                     $this->cc,
                     $this->bcc,
                     $this->Subject,
                     $body,
-                    $this->From
+                    $this->From,
+                    []
                 );
-                if ($result != 0) {
-                    throw new phpmailerException($this->lang('execute') . $this->Sendmail, self::STOP_CRITICAL);
+                if (0 !== $result) {
+                    throw new \Exception($this->lang('execute') . $this->Sendmail, self::STOP_CRITICAL);
                 }
             }
         } else {
-            if (!@$mail = popen($sendmail, 'w')) {
-                throw new phpmailerException($this->lang('execute') . $this->Sendmail, self::STOP_CRITICAL);
+            $mail = @popen($sendmail, 'w');
+            if (!$mail) {
+                throw new \Exception($this->lang('execute') . $this->Sendmail, self::STOP_CRITICAL);
             }
-            fputs($mail, $header);
-            fputs($mail, $body);
+            fwrite($mail, $header);
+            fwrite($mail, $body);
             $result = pclose($mail);
             $this->doCallback(
                 ($result == 0),
@@ -1423 +1605 @@
                 $this->bcc,
                 $this->Subject,
                 $body,
-                $this->From
+                $this->From,
+                []
             );
-            if ($result != 0) {
-                throw new phpmailerException($this->lang('execute') . $this->Sendmail, self::STOP_CRITICAL);
+            if (0 !== $result) {
+                throw new \Exception($this->lang('execute') . $this->Sendmail, self::STOP_CRITICAL);
             }
         }
+
         return true;
     }
 
     /**
      * Fix CVE-2016-10033 and CVE-2016-10045 by disallowing potentially unsafe shell characters.
-     *
      * Note that escapeshellarg and escapeshellcmd are inadequate for our purposes, especially on Windows.
-     * @param string $string The string to be validated
+     *
      * @see https://github.com/PHPMailer/PHPMailer/issues/924 CVE-2016-10045 bug report
-     * @access protected
-     * @return boolean
+     *
+     * @param string $string The string to be validated
+     *
+     * @return bool
      */
     protected static function isShellSafe($string)
     {
         // Future-proof
         if (escapeshellcmd($string) !== $string
-            or !in_array(escapeshellarg($string), array("'$string'", "\"$string\""))
+            or !in_array(escapeshellarg($string), ["'$string'", "\"$string\""])
         ) {
             return false;
         }
 
         $length = strlen($string);
 
-        for ($i = 0; $i < $length; $i++) {
+        for ($i = 0; $i < $length; ++$i) {
             $c = $string[$i];
 
             // All other characters have a special meaning in at least one common shell, including = and +.
@@ -1470 +1655 @@
      * Check whether a file path is of a permitted type.
      * Used to reject URLs and phar files from functions that access local file paths,
      * such as addAttachment.
-     * @param string $path A relative or absolute path to a file.
+     *
+     * @param string $path A relative or absolute path to a file
+     *
      * @return bool
      */
     protected static function isPermittedPath($path)
@@ -1480 +1667 @@
 
     /**
      * Send mail using the PHP mail() function.
+     *
+     * @see    http://www.php.net/manual/en/book.mail.php
+     *
      * @param string $header The message headers
-     * @param string $body The message body
-     * @link http://www.php.net/manual/en/book.mail.php
-     * @throws phpmailerException
-     * @access protected
-     * @return boolean
+     * @param string $body   The message body
+     *
+     * @throws \Exception
+     *
+     * @return bool
      */
     protected function mailSend($header, $body)
     {
-        $toArr = array();
+        $toArr = [];
         foreach ($this->to as $toaddr) {
             $toArr[] = $this->addrFormat($toaddr);
         }
@@ -1497 +1687 @@
 
         $params = null;
         //This sets the SMTP envelope sender which gets turned into a return-path header by the receiver
-        if (!empty($this->Sender) and $this->validateAddress($this->Sender)) {
+        if (!empty($this->Sender) and static::validateAddress($this->Sender)) {
+            //A space after `-f` is optional, but there is a long history of its presence
+            //causing problems, so we don't use one
+            //Exim docs: http://www.exim.org/exim-html-current/doc/html/spec_html/ch-the_exim_command_line.html
+            //Sendmail docs: http://www.sendmail.org/~ca/email/man/sendmail.html
+            //Qmail docs: http://www.qmail.org/man/man8/qmail-inject.html
+            //Example problem: https://www.drupal.org/node/1057954
             // CVE-2016-10033, CVE-2016-10045: Don't pass -f if characters will be escaped.
             if (self::isShellSafe($this->Sender)) {
                 $params = sprintf('-f%s', $this->Sender);
             }
         }
-        if (!empty($this->Sender) and !ini_get('safe_mode') and $this->validateAddress($this->Sender)) {
+        if (!empty($this->Sender) and static::validateAddress($this->Sender)) {
             $old_from = ini_get('sendmail_from');
             ini_set('sendmail_from', $this->Sender);
         }
@@ -1511 +1707 @@
         if ($this->SingleTo and count($toArr) > 1) {
             foreach ($toArr as $toAddr) {
                 $result = $this->mailPassthru($toAddr, $this->Subject, $body, $header, $params);
-                $this->doCallback($result, array($toAddr), $this->cc, $this->bcc, $this->Subject, $body, $this->From);
+                $this->doCallback($result, [$toAddr], $this->cc, $this->bcc, $this->Subject, $body, $this->From, []);
             }
         } else {
             $result = $this->mailPassthru($to, $this->Subject, $body, $header, $params);
-            $this->doCallback($result, $this->to, $this->cc, $this->bcc, $this->Subject, $body, $this->From);
+            $this->doCallback($result, $this->to, $this->cc, $this->bcc, $this->Subject, $body, $this->From, []);
         }
         if (isset($old_from)) {
             ini_set('sendmail_from', $old_from);
         }
         if (!$result) {
-            throw new phpmailerException($this->lang('instantiate'), self::STOP_CRITICAL);
+            throw new \Exception($this->lang('instantiate'), self::STOP_CRITICAL);
         }
+
         return true;
     }
 
     /**
      * Get an instance to use for SMTP operations.
-     * Override this function to load your own SMTP implementation
+     * Override this function to load your own SMTP implementation,
+     * or set one with setSMTPInstance.
+     *
      * @return SMTP
      */
     public function getSMTPInstance()
     {
         if (!is_object($this->smtp)) {
-                        require_once( 'class-smtp.php' );
-            $this->smtp = new SMTP;
+            $this->smtp = new SMTP();
         }
+
+        return $this->smtp;
+    }
+
+    /**
+     * Provide an instance to use for SMTP operations.
+     *
+     * @param SMTP $smtp
+     *
+     * @return SMTP
+     */
+    public function setSMTPInstance(SMTP $smtp)
+    {
+        $this->smtp = $smtp;
+
         return $this->smtp;
     }
 
     /**
      * Send mail via SMTP.
      * Returns false if there is a bad MAIL FROM, RCPT, or DATA input.
-     * Uses the PHPMailerSMTP class by default.
-     * @see PHPMailer::getSMTPInstance() to use a different class.
+     *
+     * @see PHPMailer::setSMTPInstance() to use a different class.
+     *
+     * @uses \PHPMailer\PHPMailer\SMTP
+     *
      * @param string $header The message headers
-     * @param string $body The message body
-     * @throws phpmailerException
-     * @uses SMTP
-     * @access protected
-     * @return boolean
+     * @param string $body   The message body
+     *
+     * @throws \Exception
+     *
+     * @return bool
      */
     protected function smtpSend($header, $body)
     {
-        $bad_rcpt = array();
+        $bad_rcpt = [];
         if (!$this->smtpConnect($this->SMTPOptions)) {
-            throw new phpmailerException($this->lang('smtp_connect_failed'), self::STOP_CRITICAL);
+            throw new \Exception($this->lang('smtp_connect_failed'), self::STOP_CRITICAL);
         }
-        if (!empty($this->Sender) and $this->validateAddress($this->Sender)) {
-            $smtp_from = $this->Sender;
-        } else {
+        //Sender already validated in preSend()
+        if ('' == $this->Sender) {
             $smtp_from = $this->From;
+        } else {
+            $smtp_from = $this->Sender;
         }
         if (!$this->smtp->mail($smtp_from)) {
             $this->setError($this->lang('from_failed') . $smtp_from . ' : ' . implode(',', $this->smtp->getError()));
-            throw new phpmailerException($this->ErrorInfo, self::STOP_CRITICAL);
+            throw new \Exception($this->ErrorInfo, self::STOP_CRITICAL);
         }
 
+        $callbacks = [];
         // Attempt to send to all recipients
-        foreach (array($this->to, $this->cc, $this->bcc) as $togroup) {
+        foreach ([$this->to, $this->cc, $this->bcc] as $togroup) {
             foreach ($togroup as $to) {
                 if (!$this->smtp->recipient($to[0])) {
                     $error = $this->smtp->getError();
-                    $bad_rcpt[] = array('to' => $to[0], 'error' => $error['detail']);
+                    $bad_rcpt[] = ['to' => $to[0], 'error' => $error['detail']];
                     $isSent = false;
                 } else {
                     $isSent = true;
                 }
-                $this->doCallback($isSent, array($to[0]), array(), array(), $this->Subject, $body, $this->From);
+
+                $callbacks[] = ['issent'=>$isSent, 'to'=>$to[0]];
             }
         }
 
         // Only send the DATA command if we have viable recipients
         if ((count($this->all_recipients) > count($bad_rcpt)) and !$this->smtp->data($header . $body)) {
-            throw new phpmailerException($this->lang('data_not_accepted'), self::STOP_CRITICAL);
+            throw new \Exception($this->lang('data_not_accepted'), self::STOP_CRITICAL);
         }
+
+        $smtp_transaction_id = $this->smtp->getLastTransactionID();
+
         if ($this->SMTPKeepAlive) {
             $this->smtp->reset();
         } else {
             $this->smtp->quit();
             $this->smtp->close();
         }
+
+        foreach ($callbacks as $cb) {
+            $this->doCallback(
+                $cb['issent'],
+                [$cb['to']],
+                [],
+                [],
+                $this->Subject,
+                $body,
+                $this->From,
+                ['smtp_transaction_id' => $smtp_transaction_id]
+            );
+        }
+
         //Create error message for any bad addresses
         if (count($bad_rcpt) > 0) {
             $errstr = '';
             foreach ($bad_rcpt as $bad) {
                 $errstr .= $bad['to'] . ': ' . $bad['error'];
             }
-            throw new phpmailerException(
+            throw new \Exception(
                 $this->lang('recipients_failed') . $errstr,
                 self::STOP_CONTINUE
             );
         }
+
         return true;
     }
 
     /**
      * Initiate a connection to an SMTP server.
      * Returns false if the operation failed.
+     *
      * @param array $options An array of options compatible with stream_context_create()
-     * @uses SMTP
-     * @access public
-     * @throws phpmailerException
-     * @return boolean
+     *
+     * @throws \Exception
+     *
+     * @uses \PHPMailer\PHPMailer\SMTP
+     *
+     * @return bool
      */
     public function smtpConnect($options = null)
     {
-        if (is_null($this->smtp)) {
+        if (null === $this->smtp) {
             $this->smtp = $this->getSMTPInstance();
         }
 
         //If no options are provided, use whatever is set in the instance
-        if (is_null($options)) {
+        if (null === $options) {
             $options = $this->SMTPOptions;
         }
 
@@ -1639 +1879 @@
         $lastexception = null;
 
         foreach ($hosts as $hostentry) {
-            $hostinfo = array();
+            $hostinfo = [];
             if (!preg_match(
                 '/^((ssl|tls):\/\/)*([a-zA-Z0-9\.-]*|\[[a-fA-F0-9:]+\]):?([0-9]*)$/',
                 trim($hostentry),
                 $hostinfo
             )) {
+                static::edebug($this->lang('connect_host') . ' ' . $hostentry);
                 // Not a valid host entry
-                $this->edebug('Ignoring invalid host: ' . $hostentry);
                 continue;
             }
             // $hostinfo[2]: optional ssl or tls prefix
@@ -1654 +1894 @@
             // $hostinfo[4]: optional port number
             // The host string prefix can temporarily override the current setting for SMTPSecure
             // If it's not specified, the default value is used
+
+            //Check the host name is a valid name or IP address before trying to use it
+            if (!static::isValidHost($hostinfo[3])) {
+                static::edebug($this->lang('connect_host') . ' ' . $hostentry);
+                continue;
+            }
             $prefix = '';
             $secure = $this->SMTPSecure;
-            $tls = ($this->SMTPSecure == 'tls');
+            $tls = ('tls' == $this->SMTPSecure);
             if ('ssl' == $hostinfo[2] or ('' == $hostinfo[2] and 'ssl' == $this->SMTPSecure)) {
                 $prefix = 'ssl://';
                 $tls = false; // Can't have SSL and TLS at the same time
                 $secure = 'ssl';
-            } elseif ($hostinfo[2] == 'tls') {
+            } elseif ('tls' == $hostinfo[2]) {
                 $tls = true;
                 // tls doesn't use a prefix
                 $secure = 'tls';
             }
             //Do we need the OpenSSL extension?
-            $sslext = defined('OPENSSL_ALGO_SHA1');
+            $sslext = defined('OPENSSL_ALGO_SHA256');
             if ('tls' === $secure or 'ssl' === $secure) {
                 //Check for an OpenSSL constant rather than using extension_loaded, which is sometimes disabled
                 if (!$sslext) {
-                    throw new phpmailerException($this->lang('extension_missing').'openssl', self::STOP_CRITICAL);
+                    throw new \Exception($this->lang('extension_missing') . 'openssl', self::STOP_CRITICAL);
                 }
             }
             $host = $hostinfo[3];
             $port = $this->Port;
-            $tport = (integer)$hostinfo[4];
+            $tport = (int) $hostinfo[4];
             if ($tport > 0 and $tport < 65536) {
                 $port = $tport;
             }
@@ -1693 +1939 @@
                     // * we have openssl extension
                     // * we are not already using SSL
                     // * the server offers STARTTLS
-                    if ($this->SMTPAutoTLS and $sslext and $secure != 'ssl' and $this->smtp->getServerExt('STARTTLS')) {
+                    if ($this->SMTPAutoTLS and $sslext and 'ssl' != $secure and $this->smtp->getServerExt('STARTTLS')) {
                         $tls = true;
                     }
                     if ($tls) {
                         if (!$this->smtp->startTLS()) {
-                            throw new phpmailerException($this->lang('connect_host'));
+                            throw new \Exception($this->lang('connect_host'));
                         }
                         // We must resend EHLO after TLS negotiation
                         $this->smtp->hello($hello);
@@ -1708 +1954 @@
                             $this->Username,
                             $this->Password,
                             $this->AuthType,
-                            $this->Realm,
-                            $this->Workstation
+                            $this->oauth
                         )
                         ) {
-                            throw new phpmailerException($this->lang('authenticate'));
+                            throw new \Exception($this->lang('authenticate'));
                         }
                     }
+
                     return true;
-                } catch (phpmailerException $exc) {
+                } catch (\Exception $exc) {
                     $lastexception = $exc;
                     $this->edebug($exc->getMessage());
                     // We must have connected, but then failed TLS or Auth, so close connection nicely
@@ -1727 +1973 @@
         // If we get here, all connection attempts have failed, so close connection hard
         $this->smtp->close();
         // As we've caught all exceptions, just report whatever the last one was
-        if ($this->exceptions and !is_null($lastexception)) {
+        if ($this->exceptions and null !== $lastexception) {
             throw $lastexception;
         }
+
         return false;
     }
 
     /**
      * Close the active SMTP session if one exists.
-     * @return void
      */
     public function smtpClose()
     {
-        if (is_a($this->smtp, 'SMTP')) {
+        if (null !== $this->smtp) {
             if ($this->smtp->connected()) {
                 $this->smtp->quit();
                 $this->smtp->close();
@@ -1751 +1997 @@
      * Set the language for error messages.
      * Returns false if it cannot load the language file.
      * The default language is English.
-     * @param string $langcode ISO 639-1 2-character language code (e.g. French is "fr")
+     *
+     * @param string $langcode  ISO 639-1 2-character language code (e.g. French is "fr")
      * @param string $lang_path Path to the language file directory, with trailing separator (slash)
-     * @return boolean
-     * @access public
+     *
+     * @return bool
      */
     public function setLanguage($langcode = 'en', $lang_path = '')
     {
         // Backwards compatibility for renamed language codes
-        $renamed_langcodes = array(
+        $renamed_langcodes = [
             'br' => 'pt_br',
             'cz' => 'cs',
             'dk' => 'da',
             'no' => 'nb',
             'se' => 'sv',
-            'sr' => 'rs'
-        );
+            'rs' => 'sr',
+            'tg' => 'tl',
+        ];
 
         if (isset($renamed_langcodes[$langcode])) {
             $langcode = $renamed_langcodes[$langcode];
         }
 
         // Define full set of translatable strings in English
-        $PHPMAILER_LANG = array(
+        $PHPMAILER_LANG = [
             'authenticate' => 'SMTP Error: Could not authenticate.',
             'connect_host' => 'SMTP Error: Could not connect to SMTP host.',
             'data_not_accepted' => 'SMTP Error: data not accepted.',
@@ -1792 +2040 @@
             'smtp_connect_failed' => 'SMTP connect() failed.',
             'smtp_error' => 'SMTP server error: ',
             'variable_set' => 'Cannot set or reset variable: ',
-            'extension_missing' => 'Extension missing: '
-        );
+            'extension_missing' => 'Extension missing: ',
+        ];
         if (empty($lang_path)) {
             // Calculate an absolute path so it can work if CWD is not here
-            $lang_path = dirname(__FILE__). DIRECTORY_SEPARATOR . 'language'. DIRECTORY_SEPARATOR;
+            $lang_path = dirname(__DIR__) . DIRECTORY_SEPARATOR . 'language' . DIRECTORY_SEPARATOR;
         }
         //Validate $langcode
         if (!preg_match('/^[a-z]{2}(?:_[a-zA-Z]{2})?$/', $langcode)) {
@@ -1805 +2053 @@
         $foundlang = true;
         $lang_file = $lang_path . 'phpmailer.lang-' . $langcode . '.php';
         // There is no English translation file
-        if ($langcode != 'en') {
+        if ('en' != $langcode) {
             // Make sure language file path is readable
-            if (!self::isPermittedPath($lang_file) or !is_readable($lang_file)) {
+            if (!static::isPermittedPath($lang_file) || !file_exists($lang_file)) {
                 $foundlang = false;
             } else {
                 // Overwrite language-specific strings.
@@ -1816 +2064 @@
             }
         }
         $this->language = $PHPMAILER_LANG;
-        return (boolean)$foundlang; // Returns false if language not found
+
+        return (bool) $foundlang; // Returns false if language not found
     }
 
     /**
      * Get the array of strings for the current language.
+     *
      * @return array
      */
     public function getTranslations()
@@ -1830 +2080 @@
 
     /**
      * Create recipient headers.
-     * @access public
+     *
      * @param string $type
-     * @param array $addr An array of recipient,
-     * where each recipient is a 2-element indexed array with element 0 containing an address
-     * and element 1 containing a name, like:
-     * array(array('joe@example.com', 'Joe User'), array('zoe@example.com', 'Zoe User'))
+     * @param array  $addr An array of recipients,
+     *                     where each recipient is a 2-element indexed array with element 0 containing an address
+     *                     and element 1 containing a name, like:
+     *                     [['joe@example.com', 'Joe User'], ['zoe@example.com', 'Zoe User']]
+     *
      * @return string
      */
     public function addrAppend($type, $addr)
     {
-        $addresses = array();
+        $addresses = [];
         foreach ($addr as $address) {
             $addresses[] = $this->addrFormat($address);
         }
-        return $type . ': ' . implode(', ', $addresses) . $this->LE;
+
+        return $type . ': ' . implode(', ', $addresses) . static::$LE;
     }
 
     /**
      * Format an address for use in a message header.
-     * @access public
-     * @param array $addr A 2-element indexed array, element 0 containing an address, element 1 containing a name
-     *      like array('joe@example.com', 'Joe User')
+     *
+     * @param array $addr A 2-element indexed array, element 0 containing an address, element 1 containing a name like
+     *                    ['joe@example.com', 'Joe User']
+     *
      * @return string
      */
     public function addrFormat($addr)
     {
         if (empty($addr[1])) { // No name provided
             return $this->secureHeader($addr[0]);
-        } else {
-            return $this->encodeHeader($this->secureHeader($addr[1]), 'phrase') . ' <' . $this->secureHeader(
+        }
+
+        return $this->encodeHeader($this->secureHeader($addr[1]), 'phrase') . ' <' . $this->secureHeader(
                 $addr[0]
             ) . '>';
-        }
     }
 
     /**
@@ -1870 +2123 @@
      * For use with mailers that do not automatically perform wrapping
      * and for quoted-printable encoded messages.
      * Original written by philippe.
+     *
      * @param string $message The message to wrap
-     * @param integer $length The line length to wrap to
-     * @param boolean $qp_mode Whether to run in Quoted-Printable mode
-     * @access public
+     * @param int    $length  The line length to wrap to
+     * @param bool   $qp_mode Whether to run in Quoted-Printable mode
+     *
      * @return string
      */
     public function wrapText($message, $length, $qp_mode = false)
     {
         if ($qp_mode) {
-            $soft_break = sprintf(' =%s', $this->LE);
+            $soft_break = sprintf(' =%s', static::$LE);
         } else {
-            $soft_break = $this->LE;
+            $soft_break = static::$LE;
         }
         // If utf-8 encoding is used, we will need to make sure we don't
         // split multibyte characters when we wrap
-        $is_utf8 = (strtolower($this->CharSet) == 'utf-8');
-        $lelen = strlen($this->LE);
-        $crlflen = strlen(self::CRLF);
+        $is_utf8 = static::CHARSET_UTF8 === strtolower($this->CharSet);
+        $lelen = strlen(static::$LE);
+        $crlflen = strlen(static::$LE);
 
-        $message = $this->fixEOL($message);
+        $message = static::normalizeBreaks($message);
         //Remove a trailing line break
-        if (substr($message, -$lelen) == $this->LE) {
+        if (substr($message, -$lelen) == static::$LE) {
             $message = substr($message, 0, -$lelen);
         }
 
         //Split message into lines
-        $lines = explode($this->LE, $message);
+        $lines = explode(static::$LE, $message);
         //Message will be rebuilt in here
         $message = '';
         foreach ($lines as $line) {
@@ -1911 +2165 @@
                             $len = $space_left;
                             if ($is_utf8) {
                                 $len = $this->utf8CharBoundary($word, $len);
-                            } elseif (substr($word, $len - 1, 1) == '=') {
-                                $len--;
-                            } elseif (substr($word, $len - 2, 1) == '=') {
+                            } elseif ('=' == substr($word, $len - 1, 1)) {
+                                --$len;
+                            } elseif ('=' == substr($word, $len - 2, 1)) {
                                 $len -= 2;
                             }
                             $part = substr($word, 0, $len);
                             $word = substr($word, $len);
                             $buf .= ' ' . $part;
-                            $message .= $buf . sprintf('=%s', self::CRLF);
+                            $message .= $buf . sprintf('=%s', static::$LE);
                         } else {
                             $message .= $buf . $soft_break;
                         }
@@ -1932 +2186 @@
                         $len = $length;
                         if ($is_utf8) {
                             $len = $this->utf8CharBoundary($word, $len);
-                        } elseif (substr($word, $len - 1, 1) == '=') {
-                            $len--;
-                        } elseif (substr($word, $len - 2, 1) == '=') {
+                        } elseif ('=' == substr($word, $len - 1, 1)) {
+                            --$len;
+                        } elseif ('=' == substr($word, $len - 2, 1)) {
                             $len -= 2;
                         }
                         $part = substr($word, 0, $len);
                         $word = substr($word, $len);
 
                         if (strlen($word) > 0) {
-                            $message .= $part . sprintf('=%s', self::CRLF);
+                            $message .= $part . sprintf('=%s', static::$LE);
                         } else {
                             $buf = $part;
                         }
@@ -1953 +2207 @@
                     }
                     $buf .= $word;
 
-                    if (strlen($buf) > $length and $buf_o != '') {
+                    if (strlen($buf) > $length and '' != $buf_o) {
                         $message .= $buf_o . $soft_break;
                         $buf = $word;
                     }
                 }
                 $firstword = false;
             }
-            $message .= $buf . self::CRLF;
+            $message .= $buf . static::$LE;
         }
 
         return $message;
@@ -1970 +2224 @@
      * Find the last character boundary prior to $maxLength in a utf-8
      * quoted-printable encoded string.
      * Original written by Colin Brown.
-     * @access public
+     *
      * @param string $encodedText utf-8 QP text
-     * @param integer $maxLength Find the last character boundary prior to this length
-     * @return integer
+     * @param int    $maxLength   Find the last character boundary prior to this length
+     *
+     * @return int
      */
     public function utf8CharBoundary($encodedText, $maxLength)
     {
@@ -1992 +2247 @@
                     // If the encoded char was found at pos 0, it will fit
                     // otherwise reduce maxLength to start of the encoded char
                     if ($encodedCharPos > 0) {
-                        $maxLength = $maxLength - ($lookBack - $encodedCharPos);
+                        $maxLength -= $lookBack - $encodedCharPos;
                     }
                     $foundSplitPos = true;
                 } elseif ($dec >= 192) {
                     // First byte of a multi byte character
                     // Reduce maxLength to split at start of character
-                    $maxLength = $maxLength - ($lookBack - $encodedCharPos);
+                    $maxLength -= $lookBack - $encodedCharPos;
                     $foundSplitPos = true;
                 } elseif ($dec < 192) {
                     // Middle byte of a multi byte character, look further back
@@ -2009 +2264 @@
                 $foundSplitPos = true;
             }
         }
+
         return $maxLength;
     }
 
@@ -2017 +2273 @@
      * Wraps the message body to the number of chars set in the WordWrap property.
      * You should only do this to plain-text bodies as wrapping HTML tags may break them.
      * This is called automatically by createBody(), so you don't need to call it yourself.
-     * @access public
-     * @return void
      */
     public function setWordWrap()
     {
@@ -2041 +2295 @@
 
     /**
      * Assemble message headers.
-     * @access public
+     *
      * @return string The assembled headers
      */
     public function createHeader()
     {
         $result = '';
 
-        $result .= $this->headerLine('Date', $this->MessageDate == '' ? self::rfcDate() : $this->MessageDate);
+        $result .= $this->headerLine('Date', '' == $this->MessageDate ? self::rfcDate() : $this->MessageDate);
 
         // To be created automatically by mail()
         if ($this->SingleTo) {
-            if ($this->Mailer != 'mail') {
+            if ('mail' != $this->Mailer) {
                 foreach ($this->to as $toaddr) {
                     $this->SingleToArray[] = $this->addrFormat($toaddr);
                 }
             }
         } else {
             if (count($this->to) > 0) {
-                if ($this->Mailer != 'mail') {
+                if ('mail' != $this->Mailer) {
                     $result .= $this->addrAppend('To', $this->to);
                 }
             } elseif (count($this->cc) == 0) {
@@ -2067 +2321 @@
             }
         }
 
-        $result .= $this->addrAppend('From', array(array(trim($this->From), $this->FromName)));
+        $result .= $this->addrAppend('From', [[trim($this->From), $this->FromName]]);
 
         // sendmail and mail() extract Cc from the header before sending
         if (count($this->cc) > 0) {
@@ -2076 +2330 @@
 
         // sendmail and mail() extract Bcc from the header before sending
         if ((
-                $this->Mailer == 'sendmail' or $this->Mailer == 'qmail' or $this->Mailer == 'mail'
+                'sendmail' == $this->Mailer or 'qmail' == $this->Mailer or 'mail' == $this->Mailer
             )
             and count($this->bcc) > 0
         ) {
@@ -2088 +2342 @@
         }
 
         // mail() sets the subject itself
-        if ($this->Mailer != 'mail') {
+        if ('mail' != $this->Mailer) {
             $result .= $this->headerLine('Subject', $this->encodeHeader($this->secureHeader($this->Subject)));
         }
 
@@ -2100 +2354 @@
             $this->lastMessageID = sprintf('<%s@%s>', $this->uniqueid, $this->serverHostname());
         }
         $result .= $this->headerLine('Message-ID', $this->lastMessageID);
-        if (!is_null($this->Priority)) {
+        if (null !== $this->Priority) {
             $result .= $this->headerLine('X-Priority', $this->Priority);
         }
-        if ($this->XMailer == '') {
+        if ('' == $this->XMailer) {
             $result .= $this->headerLine(
                 'X-Mailer',
-                'PHPMailer ' . $this->Version . ' (https://github.com/PHPMailer/PHPMailer)'
+                'PHPMailer ' . self::VERSION . ' (https://github.com/PHPMailer/PHPMailer)'
             );
         } else {
             $myXmailer = trim($this->XMailer);
@@ -2115 +2369 @@
             }
         }
 
-        if ($this->ConfirmReadingTo != '') {
+        if ('' != $this->ConfirmReadingTo) {
             $result .= $this->headerLine('Disposition-Notification-To', '<' . $this->ConfirmReadingTo . '>');
         }
 
@@ -2136 +2390 @@
 
     /**
      * Get the message MIME type headers.
-     * @access public
+     *
      * @return string
      */
     public function getMailMIME()
@@ -2145 +2399 @@
         $ismultipart = true;
         switch ($this->message_type) {
             case 'inline':
-                $result .= $this->headerLine('Content-Type', 'multipart/related;');
+                $result .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_RELATED . ';');
                 $result .= $this->textLine("\tboundary=\"" . $this->boundary[1] . '"');
                 break;
             case 'attach':
             case 'inline_attach':
             case 'alt_attach':
             case 'alt_inline_attach':
-                $result .= $this->headerLine('Content-Type', 'multipart/mixed;');
+                $result .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_MIXED . ';');
                 $result .= $this->textLine("\tboundary=\"" . $this->boundary[1] . '"');
                 break;
             case 'alt':
             case 'alt_inline':
-                $result .= $this->headerLine('Content-Type', 'multipart/alternative;');
+                $result .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_ALTERNATIVE . ';');
                 $result .= $this->textLine("\tboundary=\"" . $this->boundary[1] . '"');
                 break;
             default:
@@ -2167 +2421 @@
                 break;
         }
         // RFC1341 part 5 says 7bit is assumed if not specified
-        if ($this->Encoding != '7bit') {
+        if (static::ENCODING_7BIT != $this->Encoding) {
             // RFC 2045 section 6.4 says multipart MIME parts may only use 7bit, 8bit or binary CTE
             if ($ismultipart) {
-                if ($this->Encoding == '8bit') {
-                    $result .= $this->headerLine('Content-Transfer-Encoding', '8bit');
+                if (static::ENCODING_8BIT == $this->Encoding) {
+                    $result .= $this->headerLine('Content-Transfer-Encoding', static::ENCODING_8BIT);
                 }
                 // The only remaining alternatives are quoted-printable and base64, which are both 7bit compatible
             } else {
@@ -2179 +2433 @@
             }
         }
 
-        if ($this->Mailer != 'mail') {
-            $result .= $this->LE;
+        if ('mail' != $this->Mailer) {
+            $result .= static::$LE;
         }
 
         return $result;
@@ -2190 +2444 @@
      * Returns the whole MIME message.
      * Includes complete headers and body.
      * Only valid post preSend().
+     *
      * @see PHPMailer::preSend()
-     * @access public
+     *
      * @return string
      */
     public function getSentMIMEMessage()
     {
-        return rtrim($this->MIMEHeader . $this->mailHeader, "\n\r") . self::CRLF . self::CRLF . $this->MIMEBody;
+        return rtrim($this->MIMEHeader . $this->mailHeader, "\n\r") . static::$LE . static::$LE . $this->MIMEBody;
     }
 
     /**
-     * Create unique ID
+     * Create a unique ID to use for boundaries.
+     *
      * @return string
      */
-    protected function generateId() {
-        return md5(uniqid(time()));
+    protected function generateId()
+    {
+        $len = 32; //32 bytes = 256 bits
+        if (function_exists('random_bytes')) {
+            $bytes = random_bytes($len);
+        } elseif (function_exists('openssl_random_pseudo_bytes')) {
+            $bytes = openssl_random_pseudo_bytes($len);
+        } else {
+            //Use a hash to force the length to the same as the other methods
+            $bytes = hash('sha256', uniqid((string) mt_rand(), true), true);
+        }
+
+        //We don't care about messing up base64 format here, just want a random string
+        return str_replace(['=', '+', '/'], '', base64_encode(hash('sha256', $bytes, true)));
     }
 
     /**
      * Assemble the message body.
      * Returns an empty string on failure.
-     * @access public
-     * @throws phpmailerException
+     *
+     * @throws \Exception
+     *
      * @return string The assembled message body
      */
     public function createBody()
@@ -2224 +2493 @@
         $this->boundary[3] = 'b3_' . $this->uniqueid;
 
         if ($this->sign_key_file) {
-            $body .= $this->getMailMIME() . $this->LE;
+            $body .= $this->getMailMIME() . static::$LE;
         }
 
         $this->setWordWrap();
@@ -2232 +2501 @@
         $bodyEncoding = $this->Encoding;
         $bodyCharSet = $this->CharSet;
         //Can we do a 7-bit downgrade?
-        if ($bodyEncoding == '8bit' and !$this->has8bitChars($this->Body)) {
-            $bodyEncoding = '7bit';
+        if (static::ENCODING_8BIT == $bodyEncoding and !$this->has8bitChars($this->Body)) {
+            $bodyEncoding = static::ENCODING_7BIT;
             //All ISO 8859, Windows codepage and UTF-8 charsets are ascii compatible up to 7-bit
             $bodyCharSet = 'us-ascii';
         }
         //If lines are too long, and we're not already using an encoding that will shorten them,
         //change to quoted-printable transfer encoding for the body part only
-        if ('base64' != $this->Encoding and self::hasLineLongerThanMax($this->Body)) {
-            $bodyEncoding = 'quoted-printable';
+        if (static::ENCODING_BASE64 != $this->Encoding and static::hasLineLongerThanMax($this->Body)) {
+            $bodyEncoding = static::ENCODING_QUOTED_PRINTABLE;
         }
 
         $altBodyEncoding = $this->Encoding;
         $altBodyCharSet = $this->CharSet;
         //Can we do a 7-bit downgrade?
-        if ($altBodyEncoding == '8bit' and !$this->has8bitChars($this->AltBody)) {
-            $altBodyEncoding = '7bit';
+        if (static::ENCODING_8BIT == $altBodyEncoding and !$this->has8bitChars($this->AltBody)) {
+            $altBodyEncoding = static::ENCODING_7BIT;
             //All ISO 8859, Windows codepage and UTF-8 charsets are ascii compatible up to 7-bit
             $altBodyCharSet = 'us-ascii';
         }
         //If lines are too long, and we're not already using an encoding that will shorten them,
         //change to quoted-printable transfer encoding for the alt body part only
-        if ('base64' != $altBodyEncoding and self::hasLineLongerThanMax($this->AltBody)) {
-            $altBodyEncoding = 'quoted-printable';
+        if (static::ENCODING_BASE64 != $altBodyEncoding and static::hasLineLongerThanMax($this->AltBody)) {
+            $altBodyEncoding = static::ENCODING_QUOTED_PRINTABLE;
         }
         //Use this as a preamble in all multipart message types
-        $mimepre = "This is a multi-part message in MIME format." . $this->LE . $this->LE;
+        $mimepre = 'This is a multi-part message in MIME format.' . static::$LE;
         switch ($this->message_type) {
             case 'inline':
                 $body .= $mimepre;
                 $body .= $this->getBoundary($this->boundary[1], $bodyCharSet, '', $bodyEncoding);
                 $body .= $this->encodeString($this->Body, $bodyEncoding);
-                $body .= $this->LE . $this->LE;
+                $body .= static::$LE;
                 $body .= $this->attachAll('inline', $this->boundary[1]);
                 break;
             case 'attach':
                 $body .= $mimepre;
                 $body .= $this->getBoundary($this->boundary[1], $bodyCharSet, '', $bodyEncoding);
                 $body .= $this->encodeString($this->Body, $bodyEncoding);
-                $body .= $this->LE . $this->LE;
+                $body .= static::$LE;
                 $body .= $this->attachAll('attachment', $this->boundary[1]);
                 break;
             case 'inline_attach':
                 $body .= $mimepre;
                 $body .= $this->textLine('--' . $this->boundary[1]);
-                $body .= $this->headerLine('Content-Type', 'multipart/related;');
+                $body .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_RELATED . ';');
                 $body .= $this->textLine("\tboundary=\"" . $this->boundary[2] . '"');
-                $body .= $this->LE;
+                $body .= static::$LE;
                 $body .= $this->getBoundary($this->boundary[2], $bodyCharSet, '', $bodyEncoding);
                 $body .= $this->encodeString($this->Body, $bodyEncoding);
-                $body .= $this->LE . $this->LE;
+                $body .= static::$LE;
                 $body .= $this->attachAll('inline', $this->boundary[2]);
-                $body .= $this->LE;
+                $body .= static::$LE;
                 $body .= $this->attachAll('attachment', $this->boundary[1]);
                 break;
             case 'alt':
                 $body .= $mimepre;
-                $body .= $this->getBoundary($this->boundary[1], $altBodyCharSet, 'text/plain', $altBodyEncoding);
+                $body .= $this->getBoundary($this->boundary[1], $altBodyCharSet, static::CONTENT_TYPE_PLAINTEXT, $altBodyEncoding);
                 $body .= $this->encodeString($this->AltBody, $altBodyEncoding);
-                $body .= $this->LE . $this->LE;
-                $body .= $this->getBoundary($this->boundary[1], $bodyCharSet, 'text/html', $bodyEncoding);
+                $body .= static::$LE;
+                $body .= $this->getBoundary($this->boundary[1], $bodyCharSet, static::CONTENT_TYPE_TEXT_HTML, $bodyEncoding);
                 $body .= $this->encodeString($this->Body, $bodyEncoding);
-                $body .= $this->LE . $this->LE;
+                $body .= static::$LE;
                 if (!empty($this->Ical)) {
-                    $body .= $this->getBoundary($this->boundary[1], '', 'text/calendar; method=REQUEST', '');
+                    $body .= $this->getBoundary($this->boundary[1], '', static::CONTENT_TYPE_TEXT_CALENDAR . '; method=REQUEST', '');
                     $body .= $this->encodeString($this->Ical, $this->Encoding);
-                    $body .= $this->LE . $this->LE;
+                    $body .= static::$LE;
                 }
                 $body .= $this->endBoundary($this->boundary[1]);
                 break;
             case 'alt_inline':
                 $body .= $mimepre;
-                $body .= $this->getBoundary($this->boundary[1], $altBodyCharSet, 'text/plain', $altBodyEncoding);
+                $body .= $this->getBoundary($this->boundary[1], $altBodyCharSet, static::CONTENT_TYPE_PLAINTEXT, $altBodyEncoding);
                 $body .= $this->encodeString($this->AltBody, $altBodyEncoding);
-                $body .= $this->LE . $this->LE;
+                $body .= static::$LE;
                 $body .= $this->textLine('--' . $this->boundary[1]);
-                $body .= $this->headerLine('Content-Type', 'multipart/related;');
+                $body .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_RELATED . ';');
                 $body .= $this->textLine("\tboundary=\"" . $this->boundary[2] . '"');
-                $body .= $this->LE;
-                $body .= $this->getBoundary($this->boundary[2], $bodyCharSet, 'text/html', $bodyEncoding);
+                $body .= static::$LE;
+                $body .= $this->getBoundary($this->boundary[2], $bodyCharSet, static::CONTENT_TYPE_TEXT_HTML, $bodyEncoding);
                 $body .= $this->encodeString($this->Body, $bodyEncoding);
-                $body .= $this->LE . $this->LE;
+                $body .= static::$LE;
                 $body .= $this->attachAll('inline', $this->boundary[2]);
-                $body .= $this->LE;
+                $body .= static::$LE;
                 $body .= $this->endBoundary($this->boundary[1]);
                 break;
             case 'alt_attach':
                 $body .= $mimepre;
                 $body .= $this->textLine('--' . $this->boundary[1]);
-                $body .= $this->headerLine('Content-Type', 'multipart/alternative;');
+                $body .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_ALTERNATIVE . ';');
                 $body .= $this->textLine("\tboundary=\"" . $this->boundary[2] . '"');
-                $body .= $this->LE;
-                $body .= $this->getBoundary($this->boundary[2], $altBodyCharSet, 'text/plain', $altBodyEncoding);
+                $body .= static::$LE;
+                $body .= $this->getBoundary($this->boundary[2], $altBodyCharSet, static::CONTENT_TYPE_PLAINTEXT, $altBodyEncoding);
                 $body .= $this->encodeString($this->AltBody, $altBodyEncoding);
-                $body .= $this->LE . $this->LE;
-                $body .= $this->getBoundary($this->boundary[2], $bodyCharSet, 'text/html', $bodyEncoding);
+                $body .= static::$LE;
+                $body .= $this->getBoundary($this->boundary[2], $bodyCharSet, static::CONTENT_TYPE_TEXT_HTML, $bodyEncoding);
                 $body .= $this->encodeString($this->Body, $bodyEncoding);
-                $body .= $this->LE . $this->LE;
+                $body .= static::$LE;
+                if (!empty($this->Ical)) {
+                    $body .= $this->getBoundary($this->boundary[2], '', static::CONTENT_TYPE_TEXT_CALENDAR . '; method=REQUEST', '');
+                    $body .= $this->encodeString($this->Ical, $this->Encoding);
+                }
                 $body .= $this->endBoundary($this->boundary[2]);
-                $body .= $this->LE;
+                $body .= static::$LE;
                 $body .= $this->attachAll('attachment', $this->boundary[1]);
                 break;
             case 'alt_inline_attach':
                 $body .= $mimepre;
                 $body .= $this->textLine('--' . $this->boundary[1]);
-                $body .= $this->headerLine('Content-Type', 'multipart/alternative;');
+                $body .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_ALTERNATIVE . ';');
                 $body .= $this->textLine("\tboundary=\"" . $this->boundary[2] . '"');
-                $body .= $this->LE;
-                $body .= $this->getBoundary($this->boundary[2], $altBodyCharSet, 'text/plain', $altBodyEncoding);
+                $body .= static::$LE;
+                $body .= $this->getBoundary($this->boundary[2], $altBodyCharSet, static::CONTENT_TYPE_PLAINTEXT, $altBodyEncoding);
                 $body .= $this->encodeString($this->AltBody, $altBodyEncoding);
-                $body .= $this->LE . $this->LE;
+                $body .= static::$LE;
                 $body .= $this->textLine('--' . $this->boundary[2]);
-                $body .= $this->headerLine('Content-Type', 'multipart/related;');
+                $body .= $this->headerLine('Content-Type', static::CONTENT_TYPE_MULTIPART_RELATED . ';');
                 $body .= $this->textLine("\tboundary=\"" . $this->boundary[3] . '"');
-                $body .= $this->LE;
-                $body .= $this->getBoundary($this->boundary[3], $bodyCharSet, 'text/html', $bodyEncoding);
+                $body .= static::$LE;
+                $body .= $this->getBoundary($this->boundary[3], $bodyCharSet, static::CONTENT_TYPE_TEXT_HTML, $bodyEncoding);
                 $body .= $this->encodeString($this->Body, $bodyEncoding);
-                $body .= $this->LE . $this->LE;
+                $body .= static::$LE;
                 $body .= $this->attachAll('inline', $this->boundary[3]);
-                $body .= $this->LE;
+                $body .= static::$LE;
                 $body .= $this->endBoundary($this->boundary[2]);
-                $body .= $this->LE;
+                $body .= static::$LE;
                 $body .= $this->attachAll('attachment', $this->boundary[1]);
                 break;
             default:
@@ -2365 +2638 @@
 
         if ($this->isError()) {
             $body = '';
+            if ($this->exceptions) {
+                throw new \Exception($this->lang('empty_message'), self::STOP_CRITICAL);
+            }
         } elseif ($this->sign_key_file) {
             try {
                 if (!defined('PKCS7_TEXT')) {
-                    throw new phpmailerException($this->lang('extension_missing') . 'openssl');
+                    throw new \Exception($this->lang('extension_missing') . 'openssl');
                 }
-                // @TODO would be nice to use php://temp streams here, but need to wrap for PHP < 5.1
+                // @TODO would be nice to use php://temp streams here
                 $file = tempnam(sys_get_temp_dir(), 'mail');
                 if (false === file_put_contents($file, $body)) {
-                    throw new phpmailerException($this->lang('signing') . ' Could not write temp file');
+                    throw new \Exception($this->lang('signing') . ' Could not write temp file');
                 }
                 $signed = tempnam(sys_get_temp_dir(), 'signed');
                 //Workaround for PHP bug https://bugs.php.net/bug.php?id=69197
@@ -2382 +2658 @@
                         $file,
                         $signed,
                         'file://' . realpath($this->sign_cert_file),
-                        array('file://' . realpath($this->sign_key_file), $this->sign_key_pass),
-                        null
+                        ['file://' . realpath($this->sign_key_file), $this->sign_key_pass],
+                        []
                     );
                 } else {
                     $sign = @openssl_pkcs7_sign(
                         $file,
                         $signed,
                         'file://' . realpath($this->sign_cert_file),
-                        array('file://' . realpath($this->sign_key_file), $this->sign_key_pass),
-                        null,
+                        ['file://' . realpath($this->sign_key_file), $this->sign_key_pass],
+                        [],
                         PKCS7_DETACHED,
                         $this->sign_extracerts_file
                     );
                 }
+                @unlink($file);
                 if ($sign) {
-                    @unlink($file);
                     $body = file_get_contents($signed);
                     @unlink($signed);
                     //The message returned by openssl contains both headers and body, so need to split them up
                     $parts = explode("\n\n", $body, 2);
-                    $this->MIMEHeader .= $parts[0] . $this->LE . $this->LE;
+                    $this->MIMEHeader .= $parts[0] . static::$LE . static::$LE;
                     $body = $parts[1];
                 } else {
-                    @unlink($file);
                     @unlink($signed);
-                    throw new phpmailerException($this->lang('signing') . openssl_error_string());
+                    throw new \Exception($this->lang('signing') . openssl_error_string());
                 }
-            } catch (phpmailerException $exc) {
+            } catch (\Exception $exc) {
                 $body = '';
                 if ($this->exceptions) {
                     throw $exc;
                 }
             }
         }
+
         return $body;
     }
 
     /**
      * Return the start of a message boundary.
-     * @access protected
+     *
      * @param string $boundary
      * @param string $charSet
      * @param string $contentType
      * @param string $encoding
+     *
      * @return string
      */
     protected function getBoundary($boundary, $charSet, $contentType, $encoding)
     {
         $result = '';
-        if ($charSet == '') {
+        if ('' == $charSet) {
             $charSet = $this->CharSet;
         }
-        if ($contentType == '') {
+        if ('' == $contentType) {
             $contentType = $this->ContentType;
         }
-        if ($encoding == '') {
+        if ('' == $encoding) {
             $encoding = $this->Encoding;
         }
         $result .= $this->textLine('--' . $boundary);
         $result .= sprintf('Content-Type: %s; charset=%s', $contentType, $charSet);
-        $result .= $this->LE;
+        $result .= static::$LE;
         // RFC1341 part 5 says 7bit is assumed if not specified
-        if ($encoding != '7bit') {
+        if (static::ENCODING_7BIT != $encoding) {
             $result .= $this->headerLine('Content-Transfer-Encoding', $encoding);
         }
-        $result .= $this->LE;
+        $result .= static::$LE;
 
         return $result;
     }
 
     /**
      * Return the end of a message boundary.
-     * @access protected
+     *
      * @param string $boundary
+     *
      * @return string
      */
     protected function endBoundary($boundary)
     {
-        return $this->LE . '--' . $boundary . '--' . $this->LE;
+        return static::$LE . '--' . $boundary . '--' . static::$LE;
     }
 
     /**
      * Set the message type.
      * PHPMailer only supports some preset message types, not arbitrary MIME structures.
-     * @access protected
-     * @return void
      */
     protected function setMessageType()
     {
-        $type = array();
+        $type = [];
         if ($this->alternativeExists()) {
             $type[] = 'alt';
         }
@@ -2482 +2758 @@
             $type[] = 'attach';
         }
         $this->message_type = implode('_', $type);
-        if ($this->message_type == '') {
+        if ('' == $this->message_type) {
             //The 'plain' message_type refers to the message having a single body element, not that it is plain-text
             $this->message_type = 'plain';
         }
@@ -2490 +2766 @@
 
     /**
      * Format a header line.
-     * @access public
-     * @param string $name
-     * @param string $value
+     *
+     * @param string     $name
+     * @param string|int $value
+     *
      * @return string
      */
     public function headerLine($name, $value)
     {
-        return $name . ': ' . $value . $this->LE;
+        return $name . ': ' . $value . static::$LE;
     }
 
     /**
      * Return a formatted mail line.
-     * @access public
+     *
      * @param string $value
+     *
      * @return string
      */
     public function textLine($value)
     {
-        return $value . $this->LE;
+        return $value . static::$LE;
     }
 
     /**
@@ -2517 +2795 @@
      * Returns false if the file could not be found or read.
      * Explicitly *does not* support passing URLs; PHPMailer is not an HTTP client.
      * If you need to do that, fetch the resource yourself and pass it in via a local file or string.
-     * @param string $path Path to the attachment.
-     * @param string $name Overrides the attachment name.
-     * @param string $encoding File encoding (see $Encoding).
-     * @param string $type File extension (MIME) type.
+     *
+     * @param string $path        Path to the attachment
+     * @param string $name        Overrides the attachment name
+     * @param string $encoding    File encoding (see $Encoding)
+     * @param string $type        File extension (MIME) type
      * @param string $disposition Disposition to use
-     * @throws phpmailerException
-     * @return boolean
+     *
+     * @throws \Exception
+     *
+     * @return bool
      */
-    public function addAttachment($path, $name = '', $encoding = 'base64', $type = '', $disposition = 'attachment')
+    public function addAttachment($path, $name = '', $encoding = self::ENCODING_BASE64, $type = '', $disposition = 'attachment')
     {
         try {
-            if (!self::isPermittedPath($path) or !@is_file($path)) {
-                throw new phpmailerException($this->lang('file_access') . $path, self::STOP_CONTINUE);
+            if (!static::isPermittedPath($path) || !@is_file($path)) {
+                throw new \Exception($this->lang('file_access') . $path, self::STOP_CONTINUE);
             }
 
             // If a MIME type is not specified, try to work it out from the file name
-            if ($type == '') {
-                $type = self::filenameToType($path);
+            if ('' == $type) {
+                $type = static::filenameToType($path);
             }
 
             $filename = basename($path);
-            if ($name == '') {
+            if ('' == $name) {
                 $name = $filename;
             }
 
-            $this->attachment[] = array(
+            $this->attachment[] = [
                 0 => $path,
                 1 => $filename,
                 2 => $name,
@@ -2550 +2831 @@
                 4 => $type,
                 5 => false, // isStringAttachment
                 6 => $disposition,
-                7 => 0
-            );
-
-        } catch (phpmailerException $exc) {
+                7 => $name,
+            ];
+        } catch (\Exception $exc) {
             $this->setError($exc->getMessage());
             $this->edebug($exc->getMessage());
             if ($this->exceptions) {
                 throw $exc;
             }
+
             return false;
         }
+
         return true;
     }
 
     /**
      * Return the array of attachments.
+     *
      * @return array
      */
     public function getAttachments()
@@ -2576 +2859 @@
     /**
      * Attach all file, string, and binary attachments to the message.
      * Returns an empty string on failure.
-     * @access protected
+     *
      * @param string $disposition_type
      * @param string $boundary
+     *
      * @return string
      */
     protected function attachAll($disposition_type, $boundary)
     {
         // Return text of body
-        $mime = array();
-        $cidUniq = array();
-        $incl = array();
+        $mime = [];
+        $cidUniq = [];
+        $incl = [];
 
         // Add all attachments
         foreach ($this->attachment as $attachment) {
@@ -2602 +2886 @@
                     $path = $attachment[0];
                 }
 
-                $inclhash = md5(serialize($attachment));
+                $inclhash = hash('sha256', serialize($attachment));
                 if (in_array($inclhash, $incl)) {
                     continue;
                 }
@@ -2612 +2896 @@
                 $type = $attachment[4];
                 $disposition = $attachment[6];
                 $cid = $attachment[7];
-                if ($disposition == 'inline' && array_key_exists($cid, $cidUniq)) {
+                if ('inline' == $disposition and array_key_exists($cid, $cidUniq)) {
                     continue;
                 }
                 $cidUniq[$cid] = true;
 
-                $mime[] = sprintf('--%s%s', $boundary, $this->LE);
+                $mime[] = sprintf('--%s%s', $boundary, static::$LE);
                 //Only include a filename property if we have one
                 if (!empty($name)) {
                     $mime[] = sprintf(
                         'Content-Type: %s; name="%s"%s',
                         $type,
                         $this->encodeHeader($this->secureHeader($name)),
-                        $this->LE
+                        static::$LE
                     );
                 } else {
                     $mime[] = sprintf(
                         'Content-Type: %s%s',
                         $type,
-                        $this->LE
+                        static::$LE
                     );
                 }
                 // RFC1341 part 5 says 7bit is assumed if not specified
-                if ($encoding != '7bit') {
-                    $mime[] = sprintf('Content-Transfer-Encoding: %s%s', $encoding, $this->LE);
+                if (static::ENCODING_7BIT != $encoding) {
+                    $mime[] = sprintf('Content-Transfer-Encoding: %s%s', $encoding, static::$LE);
                 }
 
-                if ($disposition == 'inline') {
-                    $mime[] = sprintf('Content-ID: <%s>%s', $cid, $this->LE);
+                if (!empty($cid)) {
+                    $mime[] = sprintf('Content-ID: <%s>%s', $cid, static::$LE);
                 }
 
                 // If a filename contains any of these chars, it should be quoted,
@@ -2653 +2937 @@
                             'Content-Disposition: %s; filename="%s"%s',
                             $disposition,
                             $encoded_name,
-                            $this->LE . $this->LE
+                            static::$LE . static::$LE
                         );
                     } else {
                         if (!empty($encoded_name)) {
@@ -2661 +2945 @@
                                 'Content-Disposition: %s; filename=%s%s',
                                 $disposition,
                                 $encoded_name,
-                                $this->LE . $this->LE
+                                static::$LE . static::$LE
                             );
                         } else {
                             $mime[] = sprintf(
                                 'Content-Disposition: %s%s',
                                 $disposition,
-                                $this->LE . $this->LE
+                                static::$LE . static::$LE
                             );
                         }
                     }
                 } else {
-                    $mime[] = $this->LE;
+                    $mime[] = static::$LE;
                 }
 
                 // Encode as string attachment
                 if ($bString) {
                     $mime[] = $this->encodeString($string, $encoding);
-                    if ($this->isError()) {
-                        return '';
-                    }
-                    $mime[] = $this->LE . $this->LE;
                 } else {
                     $mime[] = $this->encodeFile($path, $encoding);
-                    if ($this->isError()) {
-                        return '';
-                    }
-                    $mime[] = $this->LE . $this->LE;
                 }
+                if ($this->isError()) {
+                    return '';
+                }
+                $mime[] = static::$LE;
             }
         }
 
-        $mime[] = sprintf('--%s--%s', $boundary, $this->LE);
+        $mime[] = sprintf('--%s--%s', $boundary, static::$LE);
 
         return implode('', $mime);
     }
@@ -2700 +2980 @@
     /**
      * Encode a file attachment in requested format.
      * Returns an empty string on failure.
-     * @param string $path The full path to the file
+     *
+     * @param string $path     The full path to the file
      * @param string $encoding The encoding to use; one of 'base64', '7bit', '8bit', 'binary', 'quoted-printable'
-     * @throws phpmailerException
-     * @access protected
+     *
+     * @throws \Exception
+     *
      * @return string
      */
-    protected function encodeFile($path, $encoding = 'base64')
+    protected function encodeFile($path, $encoding = self::ENCODING_BASE64)
     {
         try {
-            if (!self::isPermittedPath($path) or !file_exists($path)) {
-                throw new phpmailerException($this->lang('file_open') . $path, self::STOP_CONTINUE);
-            }
-            $magic_quotes = get_magic_quotes_runtime();
-            if ($magic_quotes) {
-                if (version_compare(PHP_VERSION, '5.3.0', '<')) {
-                    set_magic_quotes_runtime(false);
-                } else {
-                    //Doesn't exist in PHP 5.4, but we don't need to check because
-                    //get_magic_quotes_runtime always returns false in 5.4+
-                    //so it will never get here
-                    ini_set('magic_quotes_runtime', false);
-                }
+            if (!static::isPermittedPath($path) || !file_exists($path)) {
+                throw new \Exception($this->lang('file_open') . $path, self::STOP_CONTINUE);
             }
             $file_buffer = file_get_contents($path);
-            $file_buffer = $this->encodeString($file_buffer, $encoding);
-            if ($magic_quotes) {
-                if (version_compare(PHP_VERSION, '5.3.0', '<')) {
-                    set_magic_quotes_runtime($magic_quotes);
-                } else {
-                    ini_set('magic_quotes_runtime', $magic_quotes);
-                }
+            if (false === $file_buffer) {
+                throw new \Exception($this->lang('file_open') . $path, self::STOP_CONTINUE);
             }
+            $file_buffer = $this->encodeString($file_buffer, $encoding);
+
             return $file_buffer;
-        } catch (Exception $exc) {
+        } catch (\Exception $exc) {
             $this->setError($exc->getMessage());
+
             return '';
         }
     }
@@ -2742 +3011 @@
     /**
      * Encode a string in requested format.
      * Returns an empty string on failure.
-     * @param string $str The text to encode
+     *
+     * @param string $str      The text to encode
      * @param string $encoding The encoding to use; one of 'base64', '7bit', '8bit', 'binary', 'quoted-printable'
-     * @access public
+     *
      * @return string
      */
-    public function encodeString($str, $encoding = 'base64')
+    public function encodeString($str, $encoding = self::ENCODING_BASE64)
     {
         $encoded = '';
         switch (strtolower($encoding)) {
-            case 'base64':
-                $encoded = chunk_split(base64_encode($str), 76, $this->LE);
+            case static::ENCODING_BASE64:
+                $encoded = chunk_split(
+                    base64_encode($str),
+                    static::STD_LINE_LENGTH,
+                    static::$LE
+                );
                 break;
-            case '7bit':
-            case '8bit':
-                $encoded = $this->fixEOL($str);
+            case static::ENCODING_7BIT:
+            case static::ENCODING_8BIT:
+                $encoded = static::normalizeBreaks($str);
                 // Make sure it ends with a line break
-                if (substr($encoded, -(strlen($this->LE))) != $this->LE) {
-                    $encoded .= $this->LE;
+                if (substr($encoded, -(strlen(static::$LE))) != static::$LE) {
+                    $encoded .= static::$LE;
                 }
                 break;
-            case 'binary':
+            case static::ENCODING_BINARY:
                 $encoded = $str;
                 break;
-            case 'quoted-printable':
+            case static::ENCODING_QUOTED_PRINTABLE:
                 $encoded = $this->encodeQP($str);
                 break;
             default:
                 $this->setError($this->lang('encoding') . $encoding);
                 break;
         }
+
         return $encoded;
     }
 
     /**
-     * Encode a header string optimally.
-     * Picks shortest of Q, B, quoted-printable or none.
-     * @access public
-     * @param string $str
-     * @param string $position
+     * Encode a header value (not including its label) optimally.
+     * Picks shortest of Q, B, or none. Result includes folding if needed.
+     * See RFC822 definitions for phrase, comment and text positions.
+     *
+     * @param string $str      The header value to encode
+     * @param string $position What context the string will be used in
+     *
      * @return string
      */
     public function encodeHeader($str, $position = 'text')
@@ -2791 +3068 @@
                 if (!preg_match('/[\200-\377]/', $str)) {
                     // Can't use addslashes as we don't know the value of magic_quotes_sybase
                     $encoded = addcslashes($str, "\0..\37\177\\\"");
-                    if (($str == $encoded) && !preg_match('/[^A-Za-z0-9!#$%&\'*+\/=?^_`{|}~ -]/', $str)) {
-                        return ($encoded);
-                    } else {
-                        return ("\"$encoded\"");
+                    if (($str == $encoded) and !preg_match('/[^A-Za-z0-9!#$%&\'*+\/=?^_`{|}~ -]/', $str)) {
+                        return $encoded;
                     }
+
+                    return "\"$encoded\"";
                 }
                 $matchcount = preg_match_all('/[^\040\041\043-\133\135-\176]/', $str, $matches);
                 break;
-            /** @noinspection PhpMissingBreakStatementInspection */
+            /* @noinspection PhpMissingBreakStatementInspection */
             case 'comment':
                 $matchcount = preg_match_all('/[()"]/', $str, $matches);
-                // Intentional fall-through
+            //fallthrough
             case 'text':
             default:
                 $matchcount += preg_match_all('/[\000-\010\013\014\016-\037\177-\377]/', $str, $matches);
                 break;
         }
 
-        //There are no chars that need encoding
-        if ($matchcount == 0) {
-            return ($str);
-        }
-
-        $maxlen = 75 - 7 - strlen($this->CharSet);
+        //RFCs specify a maximum line length of 78 chars, however mail() will sometimes
+        //corrupt messages with headers longer than 65 chars. See #818
+        $lengthsub = 'mail' == $this->Mailer ? 13 : 0;
+        $maxlen = static::STD_LINE_LENGTH - $lengthsub;
         // Try to select the encoding which should produce the shortest output
         if ($matchcount > strlen($str) / 3) {
             // More than a third of the content will need encoding, so B encoding will be most efficient
             $encoding = 'B';
-            if (function_exists('mb_strlen') && $this->hasMultiBytes($str)) {
+            //This calculation is:
+            // max line length
+            // - shorten to avoid mail() corruption
+            // - Q/B encoding char overhead ("` =?<charset>?[QB]?<content>?=`")
+            // - charset name length
+            $maxlen = static::STD_LINE_LENGTH - $lengthsub - 8 - strlen($this->CharSet);
+            if ($this->hasMultiBytes($str)) {
                 // Use a custom function which correctly encodes and wraps long
                 // multibyte strings without breaking lines within a character
                 $encoded = $this->base64EncodeWrapMB($str, "\n");
@@ -2828 +3109 @@
                 $maxlen -= $maxlen % 4;
                 $encoded = trim(chunk_split($encoded, $maxlen, "\n"));
             }
-        } else {
+            $encoded = preg_replace('/^(.*)$/m', ' =?' . $this->CharSet . "?$encoding?\\1?=", $encoded);
+        } elseif ($matchcount > 0) {
+            //1 or more chars need encoding, use Q-encode
             $encoding = 'Q';
+            //Recalc max line length for Q encoding - see comments on B encode
+            $maxlen = static::STD_LINE_LENGTH - $lengthsub - 8 - strlen($this->CharSet);
             $encoded = $this->encodeQ($str, $position);
             $encoded = $this->wrapText($encoded, $maxlen, true);
-            $encoded = str_replace('=' . self::CRLF, "\n", trim($encoded));
+            $encoded = str_replace('=' . static::$LE, "\n", trim($encoded));
+            $encoded = preg_replace('/^(.*)$/m', ' =?' . $this->CharSet . "?$encoding?\\1?=", $encoded);
+        } elseif (strlen($str) > $maxlen) {
+            //No chars need encoding, but line is too long, so fold it
+            $encoded = trim($this->wrapText($str, $maxlen, false));
+            if ($str == $encoded) {
+                //Wrapping nicely didn't work, wrap hard instead
+                $encoded = trim(chunk_split($str, static::STD_LINE_LENGTH, static::$LE));
+            }
+            $encoded = str_replace(static::$LE, "\n", trim($encoded));
+            $encoded = preg_replace('/^(.*)$/m', ' \\1', $encoded);
+        } else {
+            //No reformatting needed
+            return $str;
         }
 
-        $encoded = preg_replace('/^(.*)$/m', ' =?' . $this->CharSet . "?$encoding?\\1?=", $encoded);
-        $encoded = trim(str_replace("\n", $this->LE, $encoded));
-
-        return $encoded;
+        return trim(static::normalizeBreaks($encoded));
     }
 
     /**
      * Check if a string contains multi-byte characters.
-     * @access public
+     *
      * @param string $str multi-byte text to wrap encode
-     * @return boolean
+     *
+     * @return bool
      */
     public function hasMultiBytes($str)
     {
         if (function_exists('mb_strlen')) {
-            return (strlen($str) > mb_strlen($str, $this->CharSet));
-        } else { // Assume no multibytes (we can't handle without mbstring functions anyway)
-            return false;
+            return strlen($str) > mb_strlen($str, $this->CharSet);
         }
+
+        // Assume no multibytes (we can't handle without mbstring functions anyway)
+        return false;
     }
 
     /**
      * Does a string contain any 8-bit chars (in any charset)?
+     *
      * @param string $text
-     * @return boolean
+     *
+     * @return bool
      */
     public function has8bitChars($text)
     {
-        return (boolean)preg_match('/[\x80-\xFF]/', $text);
+        return (bool) preg_match('/[\x80-\xFF]/', $text);
     }
 
     /**
      * Encode and wrap long multibyte strings for mail headers
      * without breaking lines within a character.
-     * Adapted from a function by paravoid
-     * @link http://www.php.net/manual/en/function.mb-encode-mimeheader.php#60283
-     * @access public
-     * @param string $str multi-byte text to wrap encode
+     * Adapted from a function by paravoid.
+     *
+     * @see http://www.php.net/manual/en/function.mb-encode-mimeheader.php#60283
+     *
+     * @param string $str       multi-byte text to wrap encode
      * @param string $linebreak string to use as linefeed/end-of-line
+     *
      * @return string
      */
     public function base64EncodeWrapMB($str, $linebreak = null)
@@ -2881 +3182 @@
         $start = '=?' . $this->CharSet . '?B?';
         $end = '?=';
         $encoded = '';
-        if ($linebreak === null) {
-            $linebreak = $this->LE;
+        if (null === $linebreak) {
+            $linebreak = static::$LE;
         }
 
         $mb_length = mb_strlen($str, $this->CharSet);
@@ -2899 +3200 @@
                 $offset = $avgLength - $lookBack;
                 $chunk = mb_substr($str, $i, $offset, $this->CharSet);
                 $chunk = base64_encode($chunk);
-                $lookBack++;
+                ++$lookBack;
             } while (strlen($chunk) > $length);
             $encoded .= $chunk . $linebreak;
         }
 
         // Chomp the last linefeed
-        $encoded = substr($encoded, 0, -strlen($linebreak));
-        return $encoded;
+        return substr($encoded, 0, -strlen($linebreak));
     }
 
     /**
      * Encode a string in quoted-printable format.
      * According to RFC2045 section 6.7.
-     * @access public
+     *
      * @param string $string The text to encode
-     * @param integer $line_max Number of chars allowed on a line before wrapping
+     *
      * @return string
-     * @link http://www.php.net/manual/en/function.quoted-printable-decode.php#89417 Adapted from this comment
      */
-    public function encodeQP($string, $line_max = 76)
+    public function encodeQP($string)
     {
-        // Use native function if it's available (>= PHP5.3)
-        if (function_exists('quoted_printable_encode')) {
-            return quoted_printable_encode($string);
-        }
-        // Fall back to a pure PHP implementation
-        $string = str_replace(
-            array('%20', '%0D%0A.', '%0D%0A', '%'),
-            array(' ', "\r\n=2E", "\r\n", '='),
-            rawurlencode($string)
-        );
-        return preg_replace('/[^\r\n]{' . ($line_max - 3) . '}[^=\r\n]{2}/', "$0=\r\n", $string);
-    }
-
-    /**
-     * Backward compatibility wrapper for an old QP encoding function that was removed.
-     * @see PHPMailer::encodeQP()
-     * @access public
-     * @param string $string
-     * @param integer $line_max
-     * @param boolean $space_conv
-     * @return string
-     * @deprecated Use encodeQP instead.
-     */
-    public function encodeQPphp(
-        $string,
-        $line_max = 76,
-        /** @noinspection PhpUnusedParameterInspection */ $space_conv = false
-    ) {
-        return $this->encodeQP($string, $line_max);
+        return static::normalizeBreaks(quoted_printable_encode($string));
     }
 
     /**
      * Encode a string using Q encoding.
-     * @link http://tools.ietf.org/html/rfc2047
-     * @param string $str the text to encode
+     *
+     * @see http://tools.ietf.org/html/rfc2047#section-4.2
+     *
+     * @param string $str      the text to encode
      * @param string $position Where the text is going to be used, see the RFC for what that means
-     * @access public
+     *
      * @return string
      */
     public function encodeQ($str, $position = 'text')
     {
         // There should not be any EOL in the string
         $pattern = '';
-        $encoded = str_replace(array("\r", "\n"), '', $str);
+        $encoded = str_replace(["\r", "\n"], '', $str);
         switch (strtolower($position)) {
             case 'phrase':
                 // RFC 2047 section 5.3
                 $pattern = '^A-Za-z0-9!*+\/ -';
                 break;
-            /** @noinspection PhpMissingBreakStatementInspection */
+            /*
+             * RFC 2047 section 5.2.
+             * Build $pattern without including delimiters and []
+             */
+            /* @noinspection PhpMissingBreakStatementInspection */
             case 'comment':
-                // RFC 2047 section 5.2
                 $pattern = '\(\)"';
-                // intentional fall-through
-                // for this reason we build the $pattern without including delimiters and []
+            /* Intentional fall through */
             case 'text':
             default:
                 // RFC 2047 section 5.1
                 // Replace every high ascii, control, =, ? and _ characters
+                /** @noinspection SuspiciousAssignmentsInspection */
                 $pattern = '\000-\011\013\014\016-\037\075\077\137\177-\377' . $pattern;
                 break;
         }
-        $matches = array();
+        $matches = [];
         if (preg_match_all("/[{$pattern}]/", $encoded, $matches)) {
             // If the string contains an '=', make sure it's the first thing we replace
             // so as to avoid double-encoding
@@ -2995 +3271 @@
                 $encoded = str_replace($char, '=' . sprintf('%02X', ord($char)), $encoded);
             }
         }
-        // Replace every spaces to _ (more readable than =20)
+        // Replace spaces with _ (more readable than =20)
+        // RFC 2047 section 4.2(2)
         return str_replace(' ', '_', $encoded);
     }
 
@@ -3003 +3280 @@
      * Add a string or binary attachment (non-filesystem).
      * This method can be used to attach ascii or binary data,
      * such as a BLOB record from a database.
-     * @param string $string String attachment data.
-     * @param string $filename Name of the attachment.
-     * @param string $encoding File encoding (see $Encoding).
-     * @param string $type File extension (MIME) type.
+     *
+     * @param string $string      String attachment data
+     * @param string $filename    Name of the attachment
+     * @param string $encoding    File encoding (see $Encoding)
+     * @param string $type        File extension (MIME) type
      * @param string $disposition Disposition to use
-     * @return void
      */
     public function addStringAttachment(
         $string,
         $filename,
-        $encoding = 'base64',
+        $encoding = self::ENCODING_BASE64,
         $type = '',
         $disposition = 'attachment'
     ) {
         // If a MIME type is not specified, try to work it out from the file name
-        if ($type == '') {
-            $type = self::filenameToType($filename);
+        if ('' == $type) {
+            $type = static::filenameToType($filename);
         }
         // Append to $attachment array
-        $this->attachment[] = array(
+        $this->attachment[] = [
             0 => $string,
             1 => $filename,
             2 => basename($filename),
@@ -3030 +3307 @@
             4 => $type,
             5 => true, // isStringAttachment
             6 => $disposition,
-            7 => 0
-        );
+            7 => 0,
+        ];
     }
 
     /**
@@ -3042 +3319 @@
      * This is used in HTML messages that embed the images
      * the HTML refers to using the $cid value.
      * Never use a user-supplied path to a file!
-     * @param string $path Path to the attachment.
-     * @param string $cid Content ID of the attachment; Use this to reference
-     *        the content when using an embedded image in HTML.
-     * @param string $name Overrides the attachment name.
-     * @param string $encoding File encoding (see $Encoding).
-     * @param string $type File MIME type.
+     *
+     * @param string $path        Path to the attachment
+     * @param string $cid         Content ID of the attachment; Use this to reference
+     *                            the content when using an embedded image in HTML
+     * @param string $name        Overrides the attachment name
+     * @param string $encoding    File encoding (see $Encoding)
+     * @param string $type        File MIME type
      * @param string $disposition Disposition to use
-     * @return boolean True on successfully adding an attachment
+     *
+     * @return bool True on successfully adding an attachment
      */
-    public function addEmbeddedImage($path, $cid, $name = '', $encoding = 'base64', $type = '', $disposition = 'inline')
+    public function addEmbeddedImage($path, $cid, $name = '', $encoding = self::ENCODING_BASE64, $type = '', $disposition = 'inline')
     {
-        if (!self::isPermittedPath($path) or !@is_file($path)) {
+        if (!static::isPermittedPath($path) || !@is_file($path)) {
             $this->setError($this->lang('file_access') . $path);
+
             return false;
         }
 
         // If a MIME type is not specified, try to work it out from the file name
-        if ($type == '') {
-            $type = self::filenameToType($path);
+        if ('' == $type) {
+            $type = static::filenameToType($path);
         }
 
         $filename = basename($path);
-        if ($name == '') {
+        if ('' == $name) {
             $name = $filename;
         }
 
         // Append to $attachment array
-        $this->attachment[] = array(
+        $this->attachment[] = [
             0 => $path,
             1 => $filename,
             2 => $name,
@@ -3077 +3357 @@
             4 => $type,
             5 => false, // isStringAttachment
             6 => $disposition,
-            7 => $cid
-        );
+            7 => $cid,
+        ];
+
         return true;
     }
 
     /**
      * Add an embedded stringified attachment.
      * This can include images, sounds, and just about any other document type.
-     * Be sure to set the $type to an image type for images:
-     * JPEG images use 'image/jpeg', GIF uses 'image/gif', PNG uses 'image/png'.
-     * @param string $string The attachment binary data.
-     * @param string $cid Content ID of the attachment; Use this to reference
-     *        the content when using an embedded image in HTML.
-     * @param string $name
-     * @param string $encoding File encoding (see $Encoding).
-     * @param string $type MIME type.
+     * If your filename doesn't contain an extension, be sure to set the $type to an appropriate MIME type.
+     *
+     * @param string $string      The attachment binary data
+     * @param string $cid         Content ID of the attachment; Use this to reference
+     *                            the content when using an embedded image in HTML
+     * @param string $name        A filename for the attachment. If this contains an extension,
+     *                            PHPMailer will attempt to set a MIME type for the attachment.
+     *                            For example 'file.jpg' would get an 'image/jpeg' MIME type.
+     * @param string $encoding    File encoding (see $Encoding), defaults to 'base64'
+     * @param string $type        MIME type - will be used in preference to any automatically derived type
      * @param string $disposition Disposition to use
-     * @return boolean True on successfully adding an attachment
+     *
+     * @return bool True on successfully adding an attachment
      */
     public function addStringEmbeddedImage(
         $string,
         $cid,
         $name = '',
-        $encoding = 'base64',
+        $encoding = self::ENCODING_BASE64,
         $type = '',
         $disposition = 'inline'
     ) {
         // If a MIME type is not specified, try to work it out from the name
-        if ($type == '' and !empty($name)) {
-            $type = self::filenameToType($name);
+        if ('' == $type and !empty($name)) {
+            $type = static::filenameToType($name);
         }
 
         // Append to $attachment array
-        $this->attachment[] = array(
+        $this->attachment[] = [
             0 => $string,
             1 => $name,
             2 => $name,
@@ -3118 +3402 @@
             4 => $type,
             5 => true, // isStringAttachment
             6 => $disposition,
-            7 => $cid
-        );
+            7 => $cid,
+        ];
+
         return true;
     }
 
     /**
+     * Check if an embedded attachment is present with this cid.
+     *
+     * @param string $cid
+     *
+     * @return bool
+     */
+    protected function cidExists($cid)
+    {
+        foreach ($this->attachment as $attachment) {
+            if ('inline' == $attachment[6] and $cid == $attachment[7]) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
      * Check if an inline attachment is present.
-     * @access public
-     * @return boolean
+     *
+     * @return bool
      */
     public function inlineImageExists()
     {
         foreach ($this->attachment as $attachment) {
-            if ($attachment[6] == 'inline') {
+            if ('inline' == $attachment[6]) {
                 return true;
             }
         }
+
         return false;
     }
 
     /**
      * Check if an attachment (non-inline) is present.
-     * @return boolean
+     *
+     * @return bool
      */
     public function attachmentExists()
     {
         foreach ($this->attachment as $attachment) {
-            if ($attachment[6] == 'attachment') {
+            if ('attachment' == $attachment[6]) {
                 return true;
             }
         }
+
         return false;
     }
 
     /**
      * Check if this message has an alternative body set.
-     * @return boolean
+     *
+     * @return bool
      */
     public function alternativeExists()
     {
@@ -3163 +3470 @@
 
     /**
      * Clear queued addresses of given kind.
-     * @access protected
+     *
      * @param string $kind 'to', 'cc', or 'bcc'
-     * @return void
      */
     public function clearQueuedAddresses($kind)
     {
-        $RecipientsQueue = $this->RecipientsQueue;
-        foreach ($RecipientsQueue as $address => $params) {
-            if ($params[0] == $kind) {
-                unset($this->RecipientsQueue[$address]);
+        $this->RecipientsQueue = array_filter(
+            $this->RecipientsQueue,
+            function ($params) use ($kind) {
+                return $params[0] != $kind;
             }
-        }
+        );
     }
 
     /**
      * Clear all To recipients.
-     * @return void
      */
     public function clearAddresses()
     {
         foreach ($this->to as $to) {
             unset($this->all_recipients[strtolower($to[0])]);
         }
-        $this->to = array();
+        $this->to = [];
         $this->clearQueuedAddresses('to');
     }
 
     /**
      * Clear all CC recipients.
-     * @return void
      */
     public function clearCCs()
     {
         foreach ($this->cc as $cc) {
             unset($this->all_recipients[strtolower($cc[0])]);
         }
-        $this->cc = array();
+        $this->cc = [];
         $this->clearQueuedAddresses('cc');
     }
 
     /**
      * Clear all BCC recipients.
-     * @return void
      */
     public function clearBCCs()
     {
         foreach ($this->bcc as $bcc) {
             unset($this->all_recipients[strtolower($bcc[0])]);
         }
-        $this->bcc = array();
+        $this->bcc = [];
         $this->clearQueuedAddresses('bcc');
     }
 
     /**
      * Clear all ReplyTo recipients.
-     * @return void
      */
     public function clearReplyTos()
     {
-        $this->ReplyTo = array();
-        $this->ReplyToQueue = array();
+        $this->ReplyTo = [];
+        $this->ReplyToQueue = [];
     }
 
     /**
      * Clear all recipient types.
-     * @return void
      */
     public function clearAllRecipients()
     {
-        $this->to = array();
-        $this->cc = array();
-        $this->bcc = array();
-        $this->all_recipients = array();
-        $this->RecipientsQueue = array();
+        $this->to = [];
+        $this->cc = [];
+        $this->bcc = [];
+        $this->all_recipients = [];
+        $this->RecipientsQueue = [];
     }
 
     /**
      * Clear all filesystem, string, and binary attachments.
-     * @return void
      */
     public function clearAttachments()
     {
-        $this->attachment = array();
+        $this->attachment = [];
     }
 
     /**
      * Clear all custom headers.
-     * @return void
      */
     public function clearCustomHeaders()
     {
-        $this->CustomHeader = array();
+        $this->CustomHeader = [];
     }
 
     /**
      * Add an error message to the error container.
-     * @access protected
+     *
      * @param string $msg
-     * @return void
      */
     protected function setError($msg)
     {
-        $this->error_count++;
-        if ($this->Mailer == 'smtp' and !is_null($this->smtp)) {
+        ++$this->error_count;
+        if ('smtp' == $this->Mailer and null !== $this->smtp) {
             $lasterror = $this->smtp->getError();
             if (!empty($lasterror['error'])) {
                 $msg .= $this->lang('smtp_error') . $lasterror['error'];
                 if (!empty($lasterror['detail'])) {
-                    $msg .= ' Detail: '. $lasterror['detail'];
+                    $msg .= ' Detail: ' . $lasterror['detail'];
                 }
                 if (!empty($lasterror['smtp_code'])) {
                     $msg .= ' SMTP code: ' . $lasterror['smtp_code'];
@@ -3286 +3584 @@
 
     /**
      * Return an RFC 822 formatted date.
-     * @access public
+     *
      * @return string
-     * @static
      */
     public static function rfcDate()
     {
         // Set the time zone to whatever the default is to avoid 500 errors
         // Will default to UTC if it's not set properly in php.ini
         date_default_timezone_set(@date_default_timezone_get());
+
         return date('D, j M Y H:i:s O');
     }
 
     /**
      * Get the server hostname.
      * Returns 'localhost.localdomain' if unknown.
-     * @access protected
+     *
      * @return string
      */
     protected function serverHostname()
     {
-        $result = 'localhost.localdomain';
+        $result = '';
         if (!empty($this->Hostname)) {
             $result = $this->Hostname;
-        } elseif (isset($_SERVER) and array_key_exists('SERVER_NAME', $_SERVER) and !empty($_SERVER['SERVER_NAME'])) {
+        } elseif (isset($_SERVER) and array_key_exists('SERVER_NAME', $_SERVER)) {
             $result = $_SERVER['SERVER_NAME'];
-        } elseif (function_exists('gethostname') && gethostname() !== false) {
+        } elseif (function_exists('gethostname') and gethostname() !== false) {
             $result = gethostname();
         } elseif (php_uname('n') !== false) {
             $result = php_uname('n');
         }
+        if (!static::isValidHost($result)) {
+            return 'localhost.localdomain';
+        }
+
         return $result;
     }
 
     /**
+     * Validate whether a string contains a valid value to use as a hostname or IP address.
+     * IPv6 addresses must include [], e.g. `[::1]`, not just `::1`.
+     *
+     * @param string $host The host name or IP address to check
+     *
+     * @return bool
+     */
+    public static function isValidHost($host)
+    {
+        //Simple syntax limits
+        if (empty($host)
+            or !is_string($host)
+            or strlen($host) > 256
+        ) {
+            return false;
+        }
+        //Looks like a bracketed IPv6 address
+        if (trim($host, '[]') != $host) {
+            return (bool) filter_var(trim($host, '[]'), FILTER_VALIDATE_IP, FILTER_FLAG_IPV6);
+        }
+        //If removing all the dots results in a numeric string, it must be an IPv4 address.
+        //Need to check this first because otherwise things like `999.0.0.0` are considered valid host names
+        if (is_numeric(str_replace('.', '', $host))) {
+            //Is it a valid IPv4 address?
+            return (bool) filter_var($host, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4);
+        }
+        if (filter_var('http://' . $host, FILTER_VALIDATE_URL)) {
+            //Is it a syntactically valid hostname?
+            return true;
+        }
+
+        return false;
+    }
+
+    /**
      * Get an error message in the current language.
-     * @access protected
+     *
      * @param string $key
+     *
      * @return string
      */
     protected function lang($key)
@@ -3332 +3670 @@
         }
 
         if (array_key_exists($key, $this->language)) {
-            if ($key == 'smtp_connect_failed') {
+            if ('smtp_connect_failed' == $key) {
                 //Include a link to troubleshooting docs on SMTP connection failure
                 //this is by far the biggest cause of support questions
                 //but it's usually not PHPMailer's fault.
                 return $this->language[$key] . ' https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting';
             }
+
             return $this->language[$key];
-        } else {
-            //Return the key as a fallback
-            return $key;
         }
+
+        //Return the key as a fallback
+        return $key;
     }
 
     /**
      * Check if an error occurred.
-     * @access public
-     * @return boolean True if an error did occur.
+     *
+     * @return bool True if an error did occur
      */
     public function isError()
     {
-        return ($this->error_count > 0);
-    }
-
-    /**
-     * Ensure consistent line endings in a string.
-     * Changes every end of line from CRLF, CR or LF to $this->LE.
-     * @access public
-     * @param string $str String to fixEOL
-     * @return string
-     */
-    public function fixEOL($str)
-    {
-        // Normalise to \n
-        $nstr = str_replace(array("\r\n", "\r"), "\n", $str);
-        // Now convert LE as needed
-        if ($this->LE !== "\n") {
-            $nstr = str_replace("\n", $this->LE, $nstr);
-        }
-        return $nstr;
+        return $this->error_count > 0;
     }
 
     /**
      * Add a custom header.
      * $name value can be overloaded to contain
-     * both header name and value (name:value)
-     * @access public
-     * @param string $name Custom header name
-     * @param string $value Header value
-     * @return void
+     * both header name and value (name:value).
+     *
+     * @param string      $name  Custom header name
+     * @param string|null $value Header value
      */
     public function addCustomHeader($name, $value = null)
     {
-        if ($value === null) {
+        if (null === $value) {
             // Value passed in as name:value
             $this->CustomHeader[] = explode(':', $name, 2);
         } else {
-            $this->CustomHeader[] = array($name, $value);
+            $this->CustomHeader[] = [$name, $value];
         }
     }
 
     /**
      * Returns all custom headers.
+     *
      * @return array
      */
     public function getCustomHeaders()
@@ -3409 +3730 @@
      * $basedir is prepended when handling relative URLs, e.g. <img src="/images/a.png"> and must not be empty
      * will look for an image file in $basedir/images/a.png and convert it to inline.
      * If you don't provide a $basedir, relative paths will be left untouched (and thus probably break in email)
+     * Converts data-uri images into embedded attachments.
      * If you don't want to apply these transformations to your HTML, just set Body and AltBody directly.
-     * @access public
-     * @param string $message HTML message string
-     * @param string $basedir Absolute path to a base directory to prepend to relative paths to images
-     * @param boolean|callable $advanced Whether to use the internal HTML to text converter
-     *    or your own custom converter @see PHPMailer::html2text()
+     *
+     * @param string        $message  HTML message string
+     * @param string        $basedir  Absolute path to a base directory to prepend to relative paths to images
+     * @param bool|callable $advanced Whether to use the internal HTML to text converter
+     *                                or your own custom converter @see PHPMailer::html2text()
+     *
      * @return string $message The transformed message Body
      */
     public function msgHTML($message, $basedir = '', $advanced = false)
     {
         preg_match_all('/(src|background)=["\'](.*)["\']/Ui', $message, $images);
         if (array_key_exists(2, $images)) {
-            if (strlen($basedir) > 1 && substr($basedir, -1) != '/') {
+            if (strlen($basedir) > 1 && '/' != substr($basedir, -1)) {
                 // Ensure $basedir has a trailing /
                 $basedir .= '/';
             }
             foreach ($images[2] as $imgindex => $url) {
                 // Convert data URIs into embedded images
-                if (preg_match('#^data:(image[^;,]*)(;base64)?,#', $url, $match)) {
-                    $data = substr($url, strpos($url, ','));
-                    if ($match[2]) {
-                        $data = base64_decode($data);
+                //e.g. "data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw=="
+                if (preg_match('#^data:(image/(?:jpe?g|gif|png));?(base64)?,(.+)#', $url, $match)) {
+                    if (count($match) == 4 and static::ENCODING_BASE64 == $match[2]) {
+                        $data = base64_decode($match[3]);
+                    } elseif ('' == $match[2]) {
+                        $data = rawurldecode($match[3]);
                     } else {
-                        $data = rawurldecode($data);
+                        //Not recognised so leave it alone
+                        continue;
                     }
-                    $cid = md5($url) . '@phpmailer.0'; // RFC2392 S 2
-                    if ($this->addStringEmbeddedImage($data, $cid, 'embed' . $imgindex, 'base64', $match[1])) {
-                        $message = str_replace(
-                            $images[0][$imgindex],
-                            $images[1][$imgindex] . '="cid:' . $cid . '"',
-                            $message
-                        );
+                    //Hash the decoded data, not the URL so that the same data-URI image used in multiple places
+                    //will only be embedded once, even if it used a different encoding
+                    $cid = hash('sha256', $data) . '@phpmailer.0'; // RFC2392 S 2
+
+                    if (!$this->cidExists($cid)) {
+                        $this->addStringEmbeddedImage($data, $cid, 'embed' . $imgindex, static::ENCODING_BASE64, $match[1]);
                     }
+                    $message = str_replace(
+                        $images[0][$imgindex],
+                        $images[1][$imgindex] . '="cid:' . $cid . '"',
+                        $message
+                    );
                     continue;
                 }
-                if (
-                    // Only process relative URLs if a basedir is provided (i.e. no absolute local paths)
+                if (// Only process relative URLs if a basedir is provided (i.e. no absolute local paths)
                     !empty($basedir)
                     // Ignore URLs containing parent dir traversal (..)
-                    && (strpos($url, '..') === false)
+                    and (strpos($url, '..') === false)
                     // Do not change urls that are already inline images
-                    && substr($url, 0, 4) !== 'cid:'
+                    and 0 !== strpos($url, 'cid:')
                     // Do not change absolute URLs, including anonymous protocol
-                    && !preg_match('#^[a-z][a-z0-9+.-]*:?//#i', $url)
+                    and !preg_match('#^[a-z][a-z0-9+.-]*:?//#i', $url)
                 ) {
                     $filename = basename($url);
                     $directory = dirname($url);
-                    if ($directory == '.') {
+                    if ('.' == $directory) {
                         $directory = '';
                     }
-                    $cid = md5($url) . '@phpmailer.0'; // RFC2392 S 2
-                    if (strlen($directory) > 1 && substr($directory, -1) != '/') {
+                    $cid = hash('sha256', $url) . '@phpmailer.0'; // RFC2392 S 2
+                    if (strlen($basedir) > 1 and '/' != substr($basedir, -1)) {
+                        $basedir .= '/';
+                    }
+                    if (strlen($directory) > 1 and '/' != substr($directory, -1)) {
                         $directory .= '/';
                     }
                     if ($this->addEmbeddedImage(
                         $basedir . $directory . $filename,
                         $cid,
                         $filename,
-                        'base64',
-                        self::_mime_types((string)self::mb_pathinfo($filename, PATHINFO_EXTENSION))
+                        static::ENCODING_BASE64,
+                        static::_mime_types((string) static::mb_pathinfo($filename, PATHINFO_EXTENSION))
                     )
                     ) {
                         $message = preg_replace(
@@ -3481 +3813 @@
             }
         }
         $this->isHTML(true);
-        // Convert all message body line breaks to CRLF, makes quoted-printable encoding work much better
-        $this->Body = $this->normalizeBreaks($message);
-        $this->AltBody = $this->normalizeBreaks($this->html2text($message, $advanced));
+        // Convert all message body line breaks to LE, makes quoted-printable encoding work much better
+        $this->Body = static::normalizeBreaks($message);
+        $this->AltBody = static::normalizeBreaks($this->html2text($message, $advanced));
         if (!$this->alternativeExists()) {
-            $this->AltBody = 'To view this email message, open it in a program that understands HTML!' .
-                self::CRLF . self::CRLF;
+            $this->AltBody = 'This is an HTML-only message. To view it, activate HTML in your email application.'
+                . static::$LE;
         }
+
         return $this->Body;
     }
 
@@ -3495 +3828 @@
      * Convert an HTML string into plain text.
      * This is used by msgHTML().
      * Note - older versions of this function used a bundled advanced converter
-     * which was been removed for license reasons in #232.
+     * which was removed for license reasons in #232.
      * Example usage:
-     * <code>
+     *
+     * ```php
      * // Use default conversion
      * $plain = $mail->html2text($html);
      * // Use your own custom converter
@@ -3505 +3839 @@
      *     $converter = new MyHtml2text($html);
      *     return $converter->get_text();
      * });
-     * </code>
-     * @param string $html The HTML text to convert
-     * @param boolean|callable $advanced Any boolean value to use the internal converter,
-     *   or provide your own callable for custom conversion.
+     * ```
+     *
+     * @param string        $html     The HTML text to convert
+     * @param bool|callable $advanced Any boolean value to use the internal converter,
+     *                                or provide your own callable for custom conversion
+     *
      * @return string
      */
     public function html2text($html, $advanced = false)
@@ -3516 +3852 @@
         if (is_callable($advanced)) {
             return call_user_func($advanced, $html);
         }
+
         return html_entity_decode(
             trim(strip_tags(preg_replace('/<(head|title|style|script)[^>]*>.*?<\/\\1>/si', '', $html))),
             ENT_QUOTES,
@@ -3525 +3862 @@
 
     /**
      * Get the MIME type for a file extension.
+     *
      * @param string $ext File extension
-     * @access public
-     * @return string MIME type of file.
-     * @static
+     *
+     * @return string MIME type of file
      */
     public static function _mime_types($ext = '')
     {
-        $mimes = array(
-            'xl'    => 'application/excel',
-            'js'    => 'application/javascript',
-            'hqx'   => 'application/mac-binhex40',
-            'cpt'   => 'application/mac-compactpro',
-            'bin'   => 'application/macbinary',
-            'doc'   => 'application/msword',
-            'word'  => 'application/msword',
-            'xlsx'  => 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
-            'xltx'  => 'application/vnd.openxmlformats-officedocument.spreadsheetml.template',
-            'potx'  => 'application/vnd.openxmlformats-officedocument.presentationml.template',
-            'ppsx'  => 'application/vnd.openxmlformats-officedocument.presentationml.slideshow',
-            'pptx'  => 'application/vnd.openxmlformats-officedocument.presentationml.presentation',
-            'sldx'  => 'application/vnd.openxmlformats-officedocument.presentationml.slide',
-            'docx'  => 'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
-            'dotx'  => 'application/vnd.openxmlformats-officedocument.wordprocessingml.template',
-            'xlam'  => 'application/vnd.ms-excel.addin.macroEnabled.12',
-            'xlsb'  => 'application/vnd.ms-excel.sheet.binary.macroEnabled.12',
+        $mimes = [
+            'xl' => 'application/excel',
+            'js' => 'application/javascript',
+            'hqx' => 'application/mac-binhex40',
+            'cpt' => 'application/mac-compactpro',
+            'bin' => 'application/macbinary',
+            'doc' => 'application/msword',
+            'word' => 'application/msword',
+            'xlsx' => 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
+            'xltx' => 'application/vnd.openxmlformats-officedocument.spreadsheetml.template',
+            'potx' => 'application/vnd.openxmlformats-officedocument.presentationml.template',
+            'ppsx' => 'application/vnd.openxmlformats-officedocument.presentationml.slideshow',
+            'pptx' => 'application/vnd.openxmlformats-officedocument.presentationml.presentation',
+            'sldx' => 'application/vnd.openxmlformats-officedocument.presentationml.slide',
+            'docx' => 'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
+            'dotx' => 'application/vnd.openxmlformats-officedocument.wordprocessingml.template',
+            'xlam' => 'application/vnd.ms-excel.addin.macroEnabled.12',
+            'xlsb' => 'application/vnd.ms-excel.sheet.binary.macroEnabled.12',
             'class' => 'application/octet-stream',
-            'dll'   => 'application/octet-stream',
-            'dms'   => 'application/octet-stream',
-            'exe'   => 'application/octet-stream',
-            'lha'   => 'application/octet-stream',
-            'lzh'   => 'application/octet-stream',
-            'psd'   => 'application/octet-stream',
-            'sea'   => 'application/octet-stream',
-            'so'    => 'application/octet-stream',
-            'oda'   => 'application/oda',
-            'pdf'   => 'application/pdf',
-            'ai'    => 'application/postscript',
-            'eps'   => 'application/postscript',
-            'ps'    => 'application/postscript',
-            'smi'   => 'application/smil',
-            'smil'  => 'application/smil',
-            'mif'   => 'application/vnd.mif',
-            'xls'   => 'application/vnd.ms-excel',
-            'ppt'   => 'application/vnd.ms-powerpoint',
+            'dll' => 'application/octet-stream',
+            'dms' => 'application/octet-stream',
+            'exe' => 'application/octet-stream',
+            'lha' => 'application/octet-stream',
+            'lzh' => 'application/octet-stream',
+            'psd' => 'application/octet-stream',
+            'sea' => 'application/octet-stream',
+            'so' => 'application/octet-stream',
+            'oda' => 'application/oda',
+            'pdf' => 'application/pdf',
+            'ai' => 'application/postscript',
+            'eps' => 'application/postscript',
+            'ps' => 'application/postscript',
+            'smi' => 'application/smil',
+            'smil' => 'application/smil',
+            'mif' => 'application/vnd.mif',
+            'xls' => 'application/vnd.ms-excel',
+            'ppt' => 'application/vnd.ms-powerpoint',
             'wbxml' => 'application/vnd.wap.wbxml',
-            'wmlc'  => 'application/vnd.wap.wmlc',
-            'dcr'   => 'application/x-director',
-            'dir'   => 'application/x-director',
-            'dxr'   => 'application/x-director',
-            'dvi'   => 'application/x-dvi',
-            'gtar'  => 'application/x-gtar',
-            'php3'  => 'application/x-httpd-php',
-            'php4'  => 'application/x-httpd-php',
-            'php'   => 'application/x-httpd-php',
+            'wmlc' => 'application/vnd.wap.wmlc',
+            'dcr' => 'application/x-director',
+            'dir' => 'application/x-director',
+            'dxr' => 'application/x-director',
+            'dvi' => 'application/x-dvi',
+            'gtar' => 'application/x-gtar',
+            'php3' => 'application/x-httpd-php',
+            'php4' => 'application/x-httpd-php',
+            'php' => 'application/x-httpd-php',
             'phtml' => 'application/x-httpd-php',
-            'phps'  => 'application/x-httpd-php-source',
-            'swf'   => 'application/x-shockwave-flash',
-            'sit'   => 'application/x-stuffit',
-            'tar'   => 'application/x-tar',
-            'tgz'   => 'application/x-tar',
-            'xht'   => 'application/xhtml+xml',
+            'phps' => 'application/x-httpd-php-source',
+            'swf' => 'application/x-shockwave-flash',
+            'sit' => 'application/x-stuffit',
+            'tar' => 'application/x-tar',
+            'tgz' => 'application/x-tar',
+            'xht' => 'application/xhtml+xml',
             'xhtml' => 'application/xhtml+xml',
-            'zip'   => 'application/zip',
-            'mid'   => 'audio/midi',
-            'midi'  => 'audio/midi',
-            'mp2'   => 'audio/mpeg',
-            'mp3'   => 'audio/mpeg',
-            'mpga'  => 'audio/mpeg',
-            'aif'   => 'audio/x-aiff',
-            'aifc'  => 'audio/x-aiff',
-            'aiff'  => 'audio/x-aiff',
-            'ram'   => 'audio/x-pn-realaudio',
-            'rm'    => 'audio/x-pn-realaudio',
-            'rpm'   => 'audio/x-pn-realaudio-plugin',
-            'ra'    => 'audio/x-realaudio',
-            'wav'   => 'audio/x-wav',
-            'bmp'   => 'image/bmp',
-            'gif'   => 'image/gif',
-            'jpeg'  => 'image/jpeg',
-            'jpe'   => 'image/jpeg',
-            'jpg'   => 'image/jpeg',
-            'png'   => 'image/png',
-            'tiff'  => 'image/tiff',
-            'tif'   => 'image/tiff',
-            'eml'   => 'message/rfc822',
-            'css'   => 'text/css',
-            'html'  => 'text/html',
-            'htm'   => 'text/html',
+            'zip' => 'application/zip',
+            'mid' => 'audio/midi',
+            'midi' => 'audio/midi',
+            'mp2' => 'audio/mpeg',
+            'mp3' => 'audio/mpeg',
+            'm4a' => 'audio/mp4',
+            'mpga' => 'audio/mpeg',
+            'aif' => 'audio/x-aiff',
+            'aifc' => 'audio/x-aiff',
+            'aiff' => 'audio/x-aiff',
+            'ram' => 'audio/x-pn-realaudio',
+            'rm' => 'audio/x-pn-realaudio',
+            'rpm' => 'audio/x-pn-realaudio-plugin',
+            'ra' => 'audio/x-realaudio',
+            'wav' => 'audio/x-wav',
+            'mka' => 'audio/x-matroska',
+            'bmp' => 'image/bmp',
+            'gif' => 'image/gif',
+            'jpeg' => 'image/jpeg',
+            'jpe' => 'image/jpeg',
+            'jpg' => 'image/jpeg',
+            'png' => 'image/png',
+            'tiff' => 'image/tiff',
+            'tif' => 'image/tiff',
+            'webp' => 'image/webp',
+            'heif' => 'image/heif',
+            'heifs' => 'image/heif-sequence',
+            'heic' => 'image/heic',
+            'heics' => 'image/heic-sequence',
+            'eml' => 'message/rfc822',
+            'css' => 'text/css',
+            'html' => 'text/html',
+            'htm' => 'text/html',
             'shtml' => 'text/html',
-            'log'   => 'text/plain',
-            'text'  => 'text/plain',
-            'txt'   => 'text/plain',
-            'rtx'   => 'text/richtext',
-            'rtf'   => 'text/rtf',
-            'vcf'   => 'text/vcard',
+            'log' => 'text/plain',
+            'text' => 'text/plain',
+            'txt' => 'text/plain',
+            'rtx' => 'text/richtext',
+            'rtf' => 'text/rtf',
+            'vcf' => 'text/vcard',
             'vcard' => 'text/vcard',
-            'xml'   => 'text/xml',
-            'xsl'   => 'text/xml',
-            'mpeg'  => 'video/mpeg',
-            'mpe'   => 'video/mpeg',
-            'mpg'   => 'video/mpeg',
-            'mov'   => 'video/quicktime',
-            'qt'    => 'video/quicktime',
-            'rv'    => 'video/vnd.rn-realvideo',
-            'avi'   => 'video/x-msvideo',
-            'movie' => 'video/x-sgi-movie'
-        );
-        if (array_key_exists(strtolower($ext), $mimes)) {
-            return $mimes[strtolower($ext)];
+            'ics' => 'text/calendar',
+            'xml' => 'text/xml',
+            'xsl' => 'text/xml',
+            'wmv' => 'video/x-ms-wmv',
+            'mpeg' => 'video/mpeg',
+            'mpe' => 'video/mpeg',
+            'mpg' => 'video/mpeg',
+            'mp4' => 'video/mp4',
+            'm4v' => 'video/mp4',
+            'mov' => 'video/quicktime',
+            'qt' => 'video/quicktime',
+            'rv' => 'video/vnd.rn-realvideo',
+            'avi' => 'video/x-msvideo',
+            'movie' => 'video/x-sgi-movie',
+            'webm' => 'video/webm',
+            'mkv' => 'video/x-matroska',
+        ];
+        $ext = strtolower($ext);
+        if (array_key_exists($ext, $mimes)) {
+            return $mimes[$ext];
         }
+
         return 'application/octet-stream';
     }
 
     /**
      * Map a file name to a MIME type.
      * Defaults to 'application/octet-stream', i.e.. arbitrary binary data.
+     *
      * @param string $filename A file name or full path, does not need to exist as a file
+     *
      * @return string
-     * @static
      */
     public static function filenameToType($filename)
     {
@@ -3652 +4005 @@
         if (false !== $qpos) {
             $filename = substr($filename, 0, $qpos);
         }
-        $pathinfo = self::mb_pathinfo($filename);
-        return self::_mime_types($pathinfo['extension']);
+        $ext = static::mb_pathinfo($filename, PATHINFO_EXTENSION);
+
+        return static::_mime_types($ext);
     }
 
     /**
      * Multi-byte-safe pathinfo replacement.
-     * Drop-in replacement for pathinfo(), but multibyte-safe, cross-platform-safe, old-version-safe.
-     * Works similarly to the one in PHP >= 5.2.0
-     * @link http://www.php.net/manual/en/function.pathinfo.php#107461
-     * @param string $path A filename or path, does not need to exist as a file
-     * @param integer|string $options Either a PATHINFO_* constant,
-     *      or a string name to return only the specified piece, allows 'filename' to work on PHP < 5.2
+     * Drop-in replacement for pathinfo(), but multibyte- and cross-platform-safe.
+     *
+     * @see    http://www.php.net/manual/en/function.pathinfo.php#107461
+     *
+     * @param string     $path    A filename or path, does not need to exist as a file
+     * @param int|string $options Either a PATHINFO_* constant,
+     *                            or a string name to return only the specified piece
+     *
      * @return string|array
-     * @static
      */
     public static function mb_pathinfo($path, $options = null)
     {
-        $ret = array('dirname' => '', 'basename' => '', 'extension' => '', 'filename' => '');
-        $pathinfo = array();
-        if (preg_match('%^(.*?)[\\\\/]*(([^/\\\\]*?)(\.([^\.\\\\/]+?)|))[\\\\/\.]*$%im', $path, $pathinfo)) {
+        $ret = ['dirname' => '', 'basename' => '', 'extension' => '', 'filename' => ''];
+        $pathinfo = [];
+        if (preg_match('#^(.*?)[\\\\/]*(([^/\\\\]*?)(\.([^\.\\\\/]+?)|))[\\\\/\.]*$#im', $path, $pathinfo)) {
             if (array_key_exists(1, $pathinfo)) {
                 $ret['dirname'] = $pathinfo[1];
             }
@@ -3710 +4065 @@
      * Usage Example:
      * `$mail->set('SMTPSecure', 'tls');`
      *   is the same as:
-     * `$mail->SMTPSecure = 'tls';`
-     * @access public
-     * @param string $name The property name to set
-     * @param mixed $value The value to set the property to
-     * @return boolean
-     * @TODO Should this not be using the __set() magic function?
+     * `$mail->SMTPSecure = 'tls';`.
+     *
+     * @param string $name  The property name to set
+     * @param mixed  $value The value to set the property to
+     *
+     * @return bool
      */
     public function set($name, $value = '')
     {
         if (property_exists($this, $name)) {
             $this->$name = $value;
+
             return true;
-        } else {
-            $this->setError($this->lang('variable_set') . $name);
-            return false;
         }
+        $this->setError($this->lang('variable_set') . $name);
+
+        return false;
     }
 
     /**
      * Strip newlines to prevent header injection.
-     * @access public
+     *
      * @param string $str
+     *
      * @return string
      */
     public function secureHeader($str)
     {
-        return trim(str_replace(array("\r", "\n"), '', $str));
+        return trim(str_replace(["\r", "\n"], '', $str));
     }
 
     /**
      * Normalize line breaks in a string.
      * Converts UNIX LF, Mac CR and Windows CRLF line breaks into a single line break format.
      * Defaults to CRLF (for message bodies) and preserves consecutive breaks.
+     *
      * @param string $text
-     * @param string $breaktype What kind of line break to use, defaults to CRLF
+     * @param string $breaktype What kind of line break to use; defaults to static::$LE
+     *
+     * @return string
+     */
+    public static function normalizeBreaks($text, $breaktype = null)
+    {
+        if (null === $breaktype) {
+            $breaktype = static::$LE;
+        }
+        // Normalise to \n
+        $text = str_replace(["\r\n", "\r"], "\n", $text);
+        // Now convert LE as needed
+        if ("\n" !== $breaktype) {
+            $text = str_replace("\n", $breaktype, $text);
+        }
+
+        return $text;
+    }
+
+    /**
+     * Return the current line break format string.
+     *
      * @return string
-     * @access public
-     * @static
      */
-    public static function normalizeBreaks($text, $breaktype = "\r\n")
+    public static function getLE()
+    {
+        return static::$LE;
+    }
+
+    /**
+     * Set the line break format string, e.g. "\r\n".
+     *
+     * @param string $le
+     */
+    protected static function setLE($le)
     {
-        return preg_replace('/(\r\n|\r|\n)/ms', $breaktype, $text);
+        static::$LE = $le;
     }
 
     /**
      * Set the public and private key files and password for S/MIME signing.
-     * @access public
+     *
      * @param string $cert_filename
      * @param string $key_filename
-     * @param string $key_pass Password for private key
+     * @param string $key_pass            Password for private key
      * @param string $extracerts_filename Optional path to chain certificate
      */
     public function sign($cert_filename, $key_filename, $key_pass, $extracerts_filename = '')
@@ -3772 +4159 @@
 
     /**
      * Quoted-Printable-encode a DKIM header.
-     * @access public
+     *
      * @param string $txt
+     *
      * @return string
      */
     public function DKIM_QP($txt)
     {
         $line = '';
-        for ($i = 0; $i < strlen($txt); $i++) {
+        $len = strlen($txt);
+        for ($i = 0; $i < $len; ++$i) {
             $ord = ord($txt[$i]);
-            if (((0x21 <= $ord) && ($ord <= 0x3A)) || $ord == 0x3C || ((0x3E <= $ord) && ($ord <= 0x7E))) {
+            if (((0x21 <= $ord) and ($ord <= 0x3A)) or $ord == 0x3C or ((0x3E <= $ord) and ($ord <= 0x7E))) {
                 $line .= $txt[$i];
             } else {
                 $line .= '=' . sprintf('%02X', $ord);
             }
         }
+
         return $line;
     }
 
     /**
      * Generate a DKIM signature.
-     * @access public
+     *
      * @param string $signHeader
-     * @throws phpmailerException
+     *
+     * @throws \Exception
+     *
      * @return string The DKIM signature value
      */
     public function DKIM_Sign($signHeader)
     {
         if (!defined('PKCS7_TEXT')) {
             if ($this->exceptions) {
-                throw new phpmailerException($this->lang('extension_missing') . 'openssl');
+                throw new \Exception($this->lang('extension_missing') . 'openssl');
             }
+
             return '';
         }
-        $privKeyStr = !empty($this->DKIM_private_string) ? $this->DKIM_private_string : file_get_contents($this->DKIM_private);
+        $privKeyStr = !empty($this->DKIM_private_string) ?
+            $this->DKIM_private_string :
+            file_get_contents($this->DKIM_private);
         if ('' != $this->DKIM_passphrase) {
             $privKey = openssl_pkey_get_private($privKeyStr, $this->DKIM_passphrase);
         } else {
             $privKey = openssl_pkey_get_private($privKeyStr);
         }
-        //Workaround for missing digest algorithms in old PHP & OpenSSL versions
-        //@link http://stackoverflow.com/a/11117338/333340
-        if (version_compare(PHP_VERSION, '5.3.0') >= 0 and
-            in_array('sha256WithRSAEncryption', openssl_get_md_methods(true))) {
-            if (openssl_sign($signHeader, $signature, $privKey, 'sha256WithRSAEncryption')) {
-                openssl_pkey_free($privKey);
-                return base64_encode($signature);
-            }
-        } else {
-            $pinfo = openssl_pkey_get_details($privKey);
-            $hash = hash('sha256', $signHeader);
-            //'Magic' constant for SHA256 from RFC3447
-            //@link https://tools.ietf.org/html/rfc3447#page-43
-            $t = '3031300d060960864801650304020105000420' . $hash;
-            $pslen = $pinfo['bits'] / 8 - (strlen($t) / 2 + 3);
-            $eb = pack('H*', '0001' . str_repeat('FF', $pslen) . '00' . $t);
-
-            if (openssl_private_encrypt($eb, $signature, $privKey, OPENSSL_NO_PADDING)) {
-                openssl_pkey_free($privKey);
-                return base64_encode($signature);
-            }
+        if (openssl_sign($signHeader, $signature, $privKey, 'sha256WithRSAEncryption')) {
+            openssl_pkey_free($privKey);
+
+            return base64_encode($signature);
         }
         openssl_pkey_free($privKey);
+
         return '';
     }
 
     /**
      * Generate a DKIM canonicalization header.
-     * @access public
+     * Uses the 'relaxed' algorithm from RFC6376 section 3.4.2.
+     * Canonicalized headers should *always* use CRLF, regardless of mailer setting.
+     *
+     * @see    https://tools.ietf.org/html/rfc6376#section-3.4.2
+     *
      * @param string $signHeader Header
+     *
      * @return string
      */
     public function DKIM_HeaderC($signHeader)
     {
-        $signHeader = preg_replace('/\r\n\s+/', ' ', $signHeader);
+        //Unfold all header continuation lines
+        //Also collapses folded whitespace.
+        //Note PCRE \s is too broad a definition of whitespace; RFC5322 defines it as `[ \t]`
+        //@see https://tools.ietf.org/html/rfc5322#section-2.2
+        //That means this may break if you do something daft like put vertical tabs in your headers.
+        $signHeader = preg_replace('/\r\n[ \t]+/', ' ', $signHeader);
         $lines = explode("\r\n", $signHeader);
         foreach ($lines as $key => $line) {
+            //If the header is missing a :, skip it as it's invalid
+            //This is likely to happen because the explode() above will also split
+            //on the trailing LE, leaving an empty line
+            if (strpos($line, ':') === false) {
+                continue;
+            }
             list($heading, $value) = explode(':', $line, 2);
+            //Lower-case header name
             $heading = strtolower($heading);
-            $value = preg_replace('/\s{2,}/', ' ', $value); // Compress useless spaces
-            $lines[$key] = $heading . ':' . trim($value); // Don't forget to remove WSP around the value
+            //Collapse white space within the value
+            $value = preg_replace('/[ \t]{2,}/', ' ', $value);
+            //RFC6376 is slightly unclear here - it says to delete space at the *end* of each value
+            //But then says to delete space before and after the colon.
+            //Net result is the same as trimming both ends of the value.
+            //by elimination, the same applies to the field name
+            $lines[$key] = trim($heading, " \t") . ':' . trim($value, " \t");
         }
-        $signHeader = implode("\r\n", $lines);
-        return $signHeader;
+
+        return implode("\r\n", $lines);
     }
 
     /**
      * Generate a DKIM canonicalization body.
-     * @access public
+     * Uses the 'simple' algorithm from RFC6376 section 3.4.3.
+     * Canonicalized bodies should *always* use CRLF, regardless of mailer setting.
+     *
+     * @see    https://tools.ietf.org/html/rfc6376#section-3.4.3
+     *
      * @param string $body Message Body
+     *
      * @return string
      */
     public function DKIM_BodyC($body)
     {
-        if ($body == '') {
+        if (empty($body)) {
             return "\r\n";
         }
-        // stabilize line endings
-        $body = str_replace("\r\n", "\n", $body);
-        $body = str_replace("\n", "\r\n", $body);
-        // END stabilize line endings
-        while (substr($body, strlen($body) - 4, 4) == "\r\n\r\n") {
-            $body = substr($body, 0, strlen($body) - 2);
-        }
-        return $body;
+        // Normalize line endings to CRLF
+        $body = static::normalizeBreaks($body, "\r\n");
+
+        //Reduce multiple trailing line breaks to a single one
+        return rtrim($body, "\r\n") . "\r\n";
     }
 
     /**
      * Create the DKIM header and body in a new message header.
-     * @access public
+     *
      * @param string $headers_line Header lines
-     * @param string $subject Subject
-     * @param string $body Body
+     * @param string $subject      Subject
+     * @param string $body         Body
+     *
      * @return string
      */
     public function DKIM_Add($headers_line, $subject, $body)
@@ -3893 +4297 @@
         $DKIMquery = 'dns/txt'; // Query method
         $DKIMtime = time(); // Signature Timestamp = seconds since 00:00:00 - Jan 1, 1970 (UTC time zone)
         $subject_header = "Subject: $subject";
-        $headers = explode($this->LE, $headers_line);
+        $headers = explode(static::$LE, $headers_line);
         $from_header = '';
         $to_header = '';
         $date_header = '';
         $current = '';
+        $copiedHeaderFields = '';
+        $foundExtraHeaders = [];
+        $extraHeaderKeys = '';
+        $extraHeaderValues = '';
+        $extraCopyHeaderFields = '';
         foreach ($headers as $header) {
             if (strpos($header, 'From:') === 0) {
                 $from_header = $header;
@@ -3908 +4317 @@
             } elseif (strpos($header, 'Date:') === 0) {
                 $date_header = $header;
                 $current = 'date_header';
+            } elseif (!empty($this->DKIM_extraHeaders)) {
+                foreach ($this->DKIM_extraHeaders as $extraHeader) {
+                    if (strpos($header, $extraHeader . ':') === 0) {
+                        $headerValue = $header;
+                        foreach ($this->CustomHeader as $customHeader) {
+                            if ($customHeader[0] === $extraHeader) {
+                                $headerValue = trim($customHeader[0]) .
+                                               ': ' .
+                                               $this->encodeHeader(trim($customHeader[1]));
+                                break;
+                            }
+                        }
+                        $foundExtraHeaders[$extraHeader] = $headerValue;
+                        $current = '';
+                        break;
+                    }
+                }
             } else {
-                if (!empty($$current) && strpos($header, ' =?') === 0) {
+                if (!empty($$current) and strpos($header, ' =?') === 0) {
                     $$current .= $header;
                 } else {
                     $current = '';
                 }
             }
         }
-        $from = str_replace('|', '=7C', $this->DKIM_QP($from_header));
-        $to = str_replace('|', '=7C', $this->DKIM_QP($to_header));
-        $date = str_replace('|', '=7C', $this->DKIM_QP($date_header));
-        $subject = str_replace(
-            '|',
-            '=7C',
-            $this->DKIM_QP($subject_header)
-        ); // Copied header fields (dkim-quoted-printable)
+        foreach ($foundExtraHeaders as $key => $value) {
+            $extraHeaderKeys .= ':' . $key;
+            $extraHeaderValues .= $value . "\r\n";
+            if ($this->DKIM_copyHeaderFields) {
+                $extraCopyHeaderFields .= "\t|" . str_replace('|', '=7C', $this->DKIM_QP($value)) . ";\r\n";
+            }
+        }
+        if ($this->DKIM_copyHeaderFields) {
+            $from = str_replace('|', '=7C', $this->DKIM_QP($from_header));
+            $to = str_replace('|', '=7C', $this->DKIM_QP($to_header));
+            $date = str_replace('|', '=7C', $this->DKIM_QP($date_header));
+            $subject = str_replace('|', '=7C', $this->DKIM_QP($subject_header));
+            $copiedHeaderFields = "\tz=$from\r\n" .
+                                  "\t|$to\r\n" .
+                                  "\t|$date\r\n" .
+                                  "\t|$subject;\r\n" .
+                                  $extraCopyHeaderFields;
+        }
         $body = $this->DKIM_BodyC($body);
         $DKIMlen = strlen($body); // Length of body
         $DKIMb64 = base64_encode(pack('H*', hash('sha256', $body))); // Base64 of packed binary SHA-256 hash of body
@@ -3939 +4375 @@
             $this->DKIM_selector .
             ";\r\n" .
             "\tt=" . $DKIMtime . '; c=' . $DKIMcanonicalization . ";\r\n" .
-            "\th=From:To:Date:Subject;\r\n" .
+            "\th=From:To:Date:Subject" . $extraHeaderKeys . ";\r\n" .
             "\td=" . $this->DKIM_domain . ';' . $ident . "\r\n" .
-            "\tz=$from\r\n" .
-            "\t|$to\r\n" .
-            "\t|$date\r\n" .
-            "\t|$subject;\r\n" .
+            $copiedHeaderFields .
             "\tbh=" . $DKIMb64 . ";\r\n" .
             "\tb=";
         $toSign = $this->DKIM_HeaderC(
@@ -3952 +4385 @@
             $to_header . "\r\n" .
             $date_header . "\r\n" .
             $subject_header . "\r\n" .
+            $extraHeaderValues .
             $dkimhdrs
         );
         $signed = $this->DKIM_Sign($toSign);
-        return $dkimhdrs . $signed . "\r\n";
+
+        return static::normalizeBreaks($dkimhdrs . $signed) . static::$LE;
     }
 
     /**
-     * Detect if a string contains a line longer than the maximum line length allowed.
+     * Detect if a string contains a line longer than the maximum line length
+     * allowed by RFC 2822 section 2.1.1.
+     *
      * @param string $str
-     * @return boolean
-     * @static
+     *
+     * @return bool
      */
     public static function hasLineLongerThanMax($str)
     {
-        //+2 to include CRLF line break for a 1000 total
-        return (boolean)preg_match('/^(.{'.(self::MAX_LINE_LENGTH + 2).',})/m', $str);
+        return (bool) preg_match('/^(.{' . (self::MAX_LINE_LENGTH + strlen(static::$LE)) . ',})/m', $str);
     }
 
     /**
      * Allows for public read access to 'to' property.
-     * @note: Before the send() call, queued addresses (i.e. with IDN) are not yet included.
-     * @access public
+     * Before the send() call, queued addresses (i.e. with IDN) are not yet included.
+     *
      * @return array
      */
     public function getToAddresses()
@@ -3983 +4419 @@
 
     /**
      * Allows for public read access to 'cc' property.
-     * @note: Before the send() call, queued addresses (i.e. with IDN) are not yet included.
-     * @access public
+     * Before the send() call, queued addresses (i.e. with IDN) are not yet included.
+     *
      * @return array
      */
     public function getCcAddresses()
@@ -3994 +4430 @@
 
     /**
      * Allows for public read access to 'bcc' property.
-     * @note: Before the send() call, queued addresses (i.e. with IDN) are not yet included.
-     * @access public
+     * Before the send() call, queued addresses (i.e. with IDN) are not yet included.
+     *
      * @return array
      */
     public function getBccAddresses()
@@ -4005 +4441 @@
 
     /**
      * Allows for public read access to 'ReplyTo' property.
-     * @note: Before the send() call, queued addresses (i.e. with IDN) are not yet included.
-     * @access public
+     * Before the send() call, queued addresses (i.e. with IDN) are not yet included.
+     *
      * @return array
      */
     public function getReplyToAddresses()
@@ -4016 +4452 @@
 
     /**
      * Allows for public read access to 'all_recipients' property.
-     * @note: Before the send() call, queued addresses (i.e. with IDN) are not yet included.
-     * @access public
+     * Before the send() call, queued addresses (i.e. with IDN) are not yet included.
+     *
      * @return array
      */
     public function getAllRecipientAddresses()
@@ -4027 +4463 @@
 
     /**
      * Perform a callback.
-     * @param boolean $isSent
-     * @param array $to
-     * @param array $cc
-     * @param array $bcc
+     *
+     * @param bool   $isSent
+     * @param array  $to
+     * @param array  $cc
+     * @param array  $bcc
      * @param string $subject
      * @param string $body
      * @param string $from
+     * @param array  $extra
      */
-    protected function doCallback($isSent, $to, $cc, $bcc, $subject, $body, $from)
+    protected function doCallback($isSent, $to, $cc, $bcc, $subject, $body, $from, $extra)
     {
-        if (!empty($this->action_function) && is_callable($this->action_function)) {
-            $params = array($isSent, $to, $cc, $bcc, $subject, $body, $from);
-            call_user_func_array($this->action_function, $params);
+        if (!empty($this->action_function) and is_callable($this->action_function)) {
+            call_user_func($this->action_function, $isSent, $to, $cc, $bcc, $subject, $body, $from, $extra);
         }
     }
-}
 
-/**
- * PHPMailer exception handler
- * @package PHPMailer
- */
-class phpmailerException extends Exception
-{
     /**
-     * Prettify error message output
-     * @return string
+     * Get the OAuth instance.
+     *
+     * @return OAuth
+     */
+    public function getOAuth()
+    {
+        return $this->oauth;
+    }
+
+    /**
+     * Set an OAuth instance.
+     *
+     * @param OAuth $oauth
      */
-    public function errorMessage()
+    public function setOAuth(OAuth $oauth)
     {
-        $errorMsg = '<strong>' . htmlspecialchars($this->getMessage()) . "</strong><br />\n";
-        return $errorMsg;
+        $this->oauth = $oauth;
     }
 }

src/wp-includes/class-smtp.php

@@ -1 +1 @@
 <?php
 /**
  * PHPMailer RFC821 SMTP email transport class.
- * PHP Version 5
- * @package PHPMailer
- * @link https://github.com/PHPMailer/PHPMailer/ The PHPMailer GitHub project
- * @author Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
- * @author Jim Jagielski (jimjag) <jimjag@gmail.com>
- * @author Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
- * @author Brent R. Matzelle (original founder)
- * @copyright 2014 Marcus Bointon
+ * PHP Version 5.5.
+ *
+ * @see       https://github.com/PHPMailer/PHPMailer/ The PHPMailer GitHub project
+ *
+ * @author    Marcus Bointon (Synchro/coolbru) <phpmailer@synchromedia.co.uk>
+ * @author    Jim Jagielski (jimjag) <jimjag@gmail.com>
+ * @author    Andy Prevost (codeworxtech) <codeworxtech@users.sourceforge.net>
+ * @author    Brent R. Matzelle (original founder)
+ * @copyright 2012 - 2017 Marcus Bointon
  * @copyright 2010 - 2012 Jim Jagielski
  * @copyright 2004 - 2009 Andy Prevost
- * @license http://www.gnu.org/copyleft/lesser.html GNU Lesser General Public License
- * @note This program is distributed in the hope that it will be useful - WITHOUT
+ * @license   http://www.gnu.org/copyleft/lesser.html GNU Lesser General Public License
+ * @note      This program is distributed in the hope that it will be useful - WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.
  */
 
+namespace PHPMailer\PHPMailer;
+
 /**
  * PHPMailer RFC821 SMTP email transport class.
  * Implements RFC 821 SMTP commands and provides some utility methods for sending mail to an SMTP server.
- * @package PHPMailer
- * @author Chris Ryan
- * @author Marcus Bointon <phpmailer@synchromedia.co.uk>
+ *
+ * @author  Chris Ryan
+ * @author  Marcus Bointon <phpmailer@synchromedia.co.uk>
  */
 class SMTP
 {
     /**
      * The PHPMailer SMTP version number.
+     *
      * @var string
      */
-    const VERSION = '5.2.27';
+    const VERSION = '6.0.7';
 
     /**
      * SMTP line break constant.
+     *
      * @var string
      */
-    const CRLF = "\r\n";
+    const LE = "\r\n";
 
     /**
      * The SMTP port to use if one is not specified.
-     * @var integer
+     *
+     * @var int
      */
-    const DEFAULT_SMTP_PORT = 25;
+    const DEFAULT_PORT = 25;
 
     /**
-     * The maximum line length allowed by RFC 2822 section 2.1.1
-     * @var integer
+     * The maximum line length allowed by RFC 2822 section 2.1.1.
+     *
+     * @var int
      */
     const MAX_LINE_LENGTH = 998;
 
     /**
-     * Debug level for no output
+     * Debug level for no output.
      */
     const DEBUG_OFF = 0;
 
     /**
-     * Debug level to show client -> server messages
+     * Debug level to show client -> server messages.
      */
     const DEBUG_CLIENT = 1;
 
     /**
-     * Debug level to show client -> server and server -> client messages
+     * Debug level to show client -> server and server -> client messages.
      */
     const DEBUG_SERVER = 2;
 
     /**
-     * Debug level to show connection status, client -> server and server -> client messages
+     * Debug level to show connection status, client -> server and server -> client messages.
      */
     const DEBUG_CONNECTION = 3;
 
     /**
-     * Debug level to show all messages
+     * Debug level to show all messages.
      */
     const DEBUG_LOWLEVEL = 4;
 
     /**
-     * The PHPMailer SMTP Version number.
-     * @var string
-     * @deprecated Use the `VERSION` constant instead
-     * @see SMTP::VERSION
-     */
-    public $Version = '5.2.27';
-
-    /**
-     * SMTP server port number.
-     * @var integer
-     * @deprecated This is only ever used as a default value, so use the `DEFAULT_SMTP_PORT` constant instead
-     * @see SMTP::DEFAULT_SMTP_PORT
-     */
-    public $SMTP_PORT = 25;
-
-    /**
-     * SMTP reply line ending.
-     * @var string
-     * @deprecated Use the `CRLF` constant instead
-     * @see SMTP::CRLF
-     */
-    public $CRLF = "\r\n";
-
-    /**
      * Debug output level.
      * Options:
      * * self::DEBUG_OFF (`0`) No debug output, default
      * * self::DEBUG_CLIENT (`1`) Client commands
      * * self::DEBUG_SERVER (`2`) Client commands and server responses
      * * self::DEBUG_CONNECTION (`3`) As DEBUG_SERVER plus connection status
-     * * self::DEBUG_LOWLEVEL (`4`) Low-level data output, all messages
-     * @var integer
+     * * self::DEBUG_LOWLEVEL (`4`) Low-level data output, all messages.
+     *
+     * @var int
      */
     public $do_debug = self::DEBUG_OFF;
 
@@ -117 +101 @@
      * * `echo` Output plain-text as-is, appropriate for CLI
      * * `html` Output escaped, line breaks converted to `<br>`, appropriate for browser output
      * * `error_log` Output to error log as configured in php.ini
-     *
      * Alternatively, you can provide a callable expecting two params: a message string and the debug level:
-     * <code>
+     *
+     * ```php
      * $smtp->Debugoutput = function($str, $level) {echo "debug level $level; message: $str";};
-     * </code>
-     * @var string|callable
+     * ```
+     *
+     * Alternatively, you can pass in an instance of a PSR-3 compatible logger, though only `debug`
+     * level output is used:
+     *
+     * ```php
+     * $mail->Debugoutput = new myPsr3Logger;
+     * ```
+     *
+     * @var string|callable|\Psr\Log\LoggerInterface
      */
     public $Debugoutput = 'echo';
 
     /**
      * Whether to use VERP.
-     * @link http://en.wikipedia.org/wiki/Variable_envelope_return_path
-     * @link http://www.postfix.org/VERP_README.html Info on VERP
-     * @var boolean
+     *
+     * @see http://en.wikipedia.org/wiki/Variable_envelope_return_path
+     * @see http://www.postfix.org/VERP_README.html Info on VERP
+     *
+     * @var bool
      */
     public $do_verp = false;
 
     /**
      * The timeout value for connection, in seconds.
-     * Default of 5 minutes (300sec) is from RFC2821 section 4.5.3.2
+     * Default of 5 minutes (300sec) is from RFC2821 section 4.5.3.2.
      * This needs to be quite high to function correctly with hosts using greetdelay as an anti-spam measure.
-     * @link http://tools.ietf.org/html/rfc2821#section-4.5.3.2
-     * @var integer
+     *
+     * @see http://tools.ietf.org/html/rfc2821#section-4.5.3.2
+     *
+     * @var int
      */
     public $Timeout = 300;
 
     /**
      * How long to wait for commands to complete, in seconds.
-     * Default of 5 minutes (300sec) is from RFC2821 section 4.5.3.2
-     * @var integer
+     * Default of 5 minutes (300sec) is from RFC2821 section 4.5.3.2.
+     *
+     * @var int
      */
     public $Timelimit = 300;
 
     /**
-     * @var array Patterns to extract an SMTP transaction id from reply to a DATA command.
+     * Patterns to extract an SMTP transaction id from reply to a DATA command.
      * The first capture group in each regex will be used as the ID.
+     * MS ESMTP returns the message ID, which may not be correct for internal tracking.
+     *
+     * @var string[]
      */
-    protected $smtp_transaction_id_patterns = array(
-        'exim' => '/[0-9]{3} OK id=(.*)/',
-        'sendmail' => '/[0-9]{3} 2.0.0 (.*) Message/',
-        'postfix' => '/[0-9]{3} 2.0.0 Ok: queued as (.*)/'
-    );
+    protected $smtp_transaction_id_patterns = [
+        'exim' => '/[\d]{3} OK id=(.*)/',
+        'sendmail' => '/[\d]{3} 2.0.0 (.*) Message/',
+        'postfix' => '/[\d]{3} 2.0.0 Ok: queued as (.*)/',
+        'Microsoft_ESMTP' => '/[0-9]{3} 2.[\d].0 (.*)@(?:.*) Queued mail for delivery/',
+        'Amazon_SES' => '/[\d]{3} Ok (.*)/',
+        'SendGrid' => '/[\d]{3} Ok: queued as (.*)/',
+        'CampaignMonitor' => '/[\d]{3} 2.0.0 OK:([a-zA-Z\d]{48})/',
+    ];
 
     /**
-     * @var string The last transaction ID issued in response to a DATA command,
-     * if one was detected
+     * The last transaction ID issued in response to a DATA command,
+     * if one was detected.
+     *
+     * @var string|bool|null
      */
     protected $last_smtp_transaction_id;
 
     /**
      * The socket for the server connection.
-     * @var resource
+     *
+     * @var ?resource
      */
     protected $smtp_conn;
 
     /**
      * Error information, if any, for the last SMTP command.
+     *
      * @var array
      */
-    protected $error = array(
+    protected $error = [
         'error' => '',
         'detail' => '',
         'smtp_code' => '',
-        'smtp_code_ex' => ''
-    );
+        'smtp_code_ex' => '',
+    ];
 
     /**
      * The reply the server sent to us for HELO.
      * If null, no HELO string has yet been received.
+     *
      * @var string|null
      */
     protected $helo_rply = null;
@@ -197 +206 @@
      * represents the server name. In case of HELO it is the only element of the array.
      * Other values can be boolean TRUE or an array containing extension options.
      * If null, no HELO/EHLO string has yet been received.
+     *
      * @var array|null
      */
     protected $server_caps = null;
 
     /**
      * The most recent reply received from the server.
+     *
      * @var string
      */
     protected $last_reply = '';
 
     /**
      * Output debugging info via a user-selected method.
+     *
+     * @param string $str   Debug string to output
+     * @param int    $level The debug level of this message; see DEBUG_* constants
+     *
      * @see SMTP::$Debugoutput
      * @see SMTP::$do_debug
-     * @param string $str Debug string to output
-     * @param integer $level The debug level of this message; see DEBUG_* constants
-     * @return void
      */
     protected function edebug($str, $level = 0)
     {
         if ($level > $this->do_debug) {
             return;
         }
+        //Is this a PSR-3 logger?
+        if ($this->Debugoutput instanceof \Psr\Log\LoggerInterface) {
+            $this->Debugoutput->debug($str);
+
+            return;
+        }
         //Avoid clash with built-in function names
-        if (!in_array($this->Debugoutput, array('error_log', 'html', 'echo')) and is_callable($this->Debugoutput)) {
+        if (!in_array($this->Debugoutput, ['error_log', 'html', 'echo']) and is_callable($this->Debugoutput)) {
             call_user_func($this->Debugoutput, $str, $level);
+
             return;
         }
         switch ($this->Debugoutput) {
@@ -232 +251 @@
                 break;
             case 'html':
                 //Cleans up output a bit for a better looking, HTML-safe output
-                echo gmdate('Y-m-d H:i:s') . ' ' . htmlentities(
+                echo gmdate('Y-m-d H:i:s'), ' ', htmlentities(
                     preg_replace('/[\r\n]+/', '', $str),
                     ENT_QUOTES,
                     'UTF-8'
-                ) . "<br>\n";
+                ), "<br>\n";
                 break;
             case 'echo':
             default:
                 //Normalize line breaks
-                $str = preg_replace('/(\r\n|\r|\n)/ms', "\n", $str);
-                echo gmdate('Y-m-d H:i:s') . "\t" . str_replace(
-                    "\n",
-                    "\n                   \t                  ",
-                    trim($str)
-                ) . "\n";
+                $str = preg_replace('/\r\n|\r/ms', "\n", $str);
+                echo gmdate('Y-m-d H:i:s'),
+                "\t",
+                    //Trim trailing space
+                trim(
+                //Indent for readability, except for trailing break
+                    str_replace(
+                        "\n",
+                        "\n                   \t                  ",
+                        trim($str)
+                    )
+                ),
+                "\n";
         }
     }
 
     /**
      * Connect to an SMTP server.
-     * @param string $host SMTP server IP or host name
-     * @param integer $port The port number to connect to
-     * @param integer $timeout How long to wait for the connection to open
-     * @param array $options An array of options for stream_context_create()
-     * @access public
-     * @return boolean
+     *
+     * @param string $host    SMTP server IP or host name
+     * @param int    $port    The port number to connect to
+     * @param int    $timeout How long to wait for the connection to open
+     * @param array  $options An array of options for stream_context_create()
+     *
+     * @return bool
      */
-    public function connect($host, $port = null, $timeout = 30, $options = array())
+    public function connect($host, $port = null, $timeout = 30, $options = [])
     {
         static $streamok;
         //This is enabled by default since 5.0.0 but some providers disable it
         //Check this once and cache the result
-        if (is_null($streamok)) {
+        if (null === $streamok) {
             $streamok = function_exists('stream_socket_client');
         }
         // Clear errors to avoid confusion
@@ -273 +300 @@
         if ($this->connected()) {
             // Already connected, generate error
             $this->setError('Already connected to a server');
+
             return false;
         }
         if (empty($port)) {
-            $port = self::DEFAULT_SMTP_PORT;
+            $port = self::DEFAULT_PORT;
         }
         // Connect to the SMTP server
         $this->edebug(
             "Connection: opening to $host:$port, timeout=$timeout, options=" .
-            var_export($options, true),
+            (count($options) > 0 ? var_export($options, true) : 'array()'),
             self::DEBUG_CONNECTION
         );
         $errno = 0;
         $errstr = '';
         if ($streamok) {
             $socket_context = stream_context_create($options);
-            set_error_handler(array($this, 'errorHandler'));
+            set_error_handler([$this, 'errorHandler']);
             $this->smtp_conn = stream_socket_client(
-                $host . ":" . $port,
+                $host . ':' . $port,
                 $errno,
                 $errstr,
                 $timeout,
@@ -301 +329 @@
         } else {
             //Fall back to fsockopen which should work in more places, but is missing some features
             $this->edebug(
-                "Connection: stream_socket_client not available, falling back to fsockopen",
+                'Connection: stream_socket_client not available, falling back to fsockopen',
                 self::DEBUG_CONNECTION
             );
-            set_error_handler(array($this, 'errorHandler'));
+            set_error_handler([$this, 'errorHandler']);
             $this->smtp_conn = fsockopen(
                 $host,
                 $port,
@@ -318 +346 @@
         if (!is_resource($this->smtp_conn)) {
             $this->setError(
                 'Failed to connect to server',
-                $errno,
-                $errstr
+                '',
+                (string) $errno,
+                (string) $errstr
             );
             $this->edebug(
                 'SMTP ERROR: ' . $this->error['error']
                 . ": $errstr ($errno)",
                 self::DEBUG_CLIENT
             );
+
             return false;
         }
         $this->edebug('Connection: opened', self::DEBUG_CONNECTION);
@@ -334 +364 @@
         if (substr(PHP_OS, 0, 3) != 'WIN') {
             $max = ini_get('max_execution_time');
             // Don't bother if unlimited
-            if ($max != 0 && $timeout > $max) {
+            if (0 != $max and $timeout > $max) {
                 @set_time_limit($timeout);
             }
             stream_set_timeout($this->smtp_conn, $timeout, 0);
@@ -342 +372 @@
         // Get any announcement
         $announce = $this->get_lines();
         $this->edebug('SERVER -> CLIENT: ' . $announce, self::DEBUG_SERVER);
+
         return true;
     }
 
     /**
      * Initiate a TLS (encrypted) session.
-     * @access public
-     * @return boolean
+     *
+     * @return bool
      */
     public function startTLS()
     {
@@ -367 +398 @@
         }
 
         // Begin encrypted connection
-        set_error_handler(array($this, 'errorHandler'));
+        set_error_handler([$this, 'errorHandler']);
         $crypto_ok = stream_socket_enable_crypto(
             $this->smtp_conn,
             true,
             $crypto_method
         );
         restore_error_handler();
-        return $crypto_ok;
+
+        return (bool) $crypto_ok;
     }
 
     /**
      * Perform SMTP authentication.
      * Must be run after hello().
-     * @see hello()
+     *
+     * @see    hello()
+     *
      * @param string $username The user name
      * @param string $password The password
-     * @param string $authtype The auth type (PLAIN, LOGIN, CRAM-MD5)
-     * @param string $realm The auth realm for NTLM
-     * @param string $workstation The auth workstation for NTLM
-     * @param null|OAuth $OAuth An optional OAuth instance (@see PHPMailerOAuth)
-     * @return bool True if successfully authenticated.* @access public
+     * @param string $authtype The auth type (CRAM-MD5, PLAIN, LOGIN, XOAUTH2)
+     * @param OAuth  $OAuth    An optional OAuth instance for XOAUTH2 authentication
+     *
+     * @return bool True if successfully authenticated
      */
     public function authenticate(
         $username,
         $password,
         $authtype = null,
-        $realm = '',
-        $workstation = '',
         $OAuth = null
     ) {
         if (!$this->server_caps) {
             $this->setError('Authentication is not allowed before HELO/EHLO');
+
             return false;
         }
 
@@ -408 +440 @@
                 $this->setError('Authentication is not allowed at this stage');
                 // 'at this stage' means that auth may be allowed after the stage changes
                 // e.g. after STARTTLS
+
                 return false;
             }
 
-            self::edebug('Auth method requested: ' . ($authtype ? $authtype : 'UNKNOWN'), self::DEBUG_LOWLEVEL);
-            self::edebug(
+            $this->edebug('Auth method requested: ' . ($authtype ? $authtype : 'UNSPECIFIED'), self::DEBUG_LOWLEVEL);
+            $this->edebug(
                 'Auth methods available on the server: ' . implode(',', $this->server_caps['AUTH']),
                 self::DEBUG_LOWLEVEL
             );
 
+            //If we have requested a specific auth type, check the server supports it before trying others
+            if (null !== $authtype and !in_array($authtype, $this->server_caps['AUTH'])) {
+                $this->edebug('Requested auth method not available: ' . $authtype, self::DEBUG_LOWLEVEL);
+                $authtype = null;
+            }
+
             if (empty($authtype)) {
-                foreach (array('CRAM-MD5', 'LOGIN', 'PLAIN') as $method) {
+                //If no auth mechanism is specified, attempt to use these, in this order
+                //Try CRAM-MD5 first as it's more secure than the others
+                foreach (['CRAM-MD5', 'LOGIN', 'PLAIN', 'XOAUTH2'] as $method) {
                     if (in_array($method, $this->server_caps['AUTH'])) {
                         $authtype = $method;
                         break;
@@ -426 +467 @@
                 }
                 if (empty($authtype)) {
                     $this->setError('No supported authentication methods found');
+
                     return false;
                 }
                 self::edebug('Auth method selected: ' . $authtype, self::DEBUG_LOWLEVEL);
@@ -433 +475 @@
 
             if (!in_array($authtype, $this->server_caps['AUTH'])) {
                 $this->setError("The requested authentication method \"$authtype\" is not supported by the server");
+
                 return false;
             }
         } elseif (empty($authtype)) {
@@ -459 +502 @@
                 if (!$this->sendCommand('AUTH', 'AUTH LOGIN', 334)) {
                     return false;
                 }
-                if (!$this->sendCommand("Username", base64_encode($username), 334)) {
+                if (!$this->sendCommand('Username', base64_encode($username), 334)) {
                     return false;
                 }
-                if (!$this->sendCommand("Password", base64_encode($password), 235)) {
+                if (!$this->sendCommand('Password', base64_encode($password), 235)) {
                     return false;
                 }
                 break;
@@ -479 +522 @@
 
                 // send encoded credentials
                 return $this->sendCommand('Username', base64_encode($response), 235);
+            case 'XOAUTH2':
+                //The OAuth instance must be set up prior to requesting auth.
+                if (null === $OAuth) {
+                    return false;
+                }
+                $oauth = $OAuth->getOauth64();
+
+                // Start authentication
+                if (!$this->sendCommand('AUTH', 'AUTH XOAUTH2 ' . $oauth, 235)) {
+                    return false;
+                }
+                break;
             default:
                 $this->setError("Authentication method \"$authtype\" is not supported");
+
                 return false;
         }
+
         return true;
     }
 
     /**
      * Calculate an MD5 HMAC hash.
      * Works like hash_hmac('md5', $data, $key)
-     * in case that function is not available
+     * in case that function is not available.
+     *
      * @param string $data The data to hash
-     * @param string $key The key to hash with
-     * @access protected
+     * @param string $key  The key to hash with
+     *
      * @return string
      */
     protected function hmac($data, $key)
@@ -524 +582 @@
 
     /**
      * Check connection state.
-     * @access public
-     * @return boolean True if connected.
+     *
+     * @return bool True if connected
      */
     public function connected()
     {
@@ -538 +596 @@
                     self::DEBUG_CLIENT
                 );
                 $this->close();
+
                 return false;
             }
+
             return true; // everything looks good
         }
+
         return false;
     }
 
     /**
      * Close the socket and clean up the state of the class.
      * Don't use this function without first trying to use QUIT.
+     *
      * @see quit()
-     * @access public
-     * @return void
      */
     public function close()
     {
@@ -571 +631 @@
      * finializing the mail transaction. $msg_data is the message
      * that is to be send with the headers. Each header needs to be
      * on a single line followed by a <CRLF> with the message headers
-     * and the message body being separated by and additional <CRLF>.
-     * Implements rfc 821: DATA <CRLF>
+     * and the message body being separated by an additional <CRLF>.
+     * Implements RFC 821: DATA <CRLF>.
+     *
      * @param string $msg_data Message data to send
-     * @access public
-     * @return boolean
+     *
+     * @return bool
      */
     public function data($msg_data)
     {
@@ -585 +646 @@
         }
 
         /* The server is ready to accept data!
-         * According to rfc821 we should not send more than 1000 characters on a single line (including the CRLF)
+         * According to rfc821 we should not send more than 1000 characters on a single line (including the LE)
          * so we will break the data up into lines by \r and/or \n then if needed we will break each of those into
          * smaller lines to fit within the limit.
          * We will also look for lines that start with a '.' and prepend an additional '.'.
@@ -593 +654 @@
          */
 
         // Normalize line breaks before exploding
-        $lines = explode("\n", str_replace(array("\r\n", "\r"), "\n", $msg_data));
+        $lines = explode("\n", str_replace(["\r\n", "\r"], "\n", $msg_data));
 
         /* To distinguish between a complete RFC822 message and a plain message body, we check if the first field
          * of the first line (':' separated) does not contain a space then it _should_ be a header and we will
@@ -602 +663 @@
 
         $field = substr($lines[0], 0, strpos($lines[0], ':'));
         $in_headers = false;
-        if (!empty($field) && strpos($field, ' ') === false) {
+        if (!empty($field) and strpos($field, ' ') === false) {
             $in_headers = true;
         }
 
         foreach ($lines as $line) {
-            $lines_out = array();
+            $lines_out = [];
             if ($in_headers and $line == '') {
                 $in_headers = false;
             }
@@ -642 +703 @@
                 if (!empty($line_out) and $line_out[0] == '.') {
                     $line_out = '.' . $line_out;
                 }
-                $this->client_send($line_out . self::CRLF);
+                $this->client_send($line_out . static::LE, 'DATA');
             }
         }
 
@@ -654 +715 @@
         $this->recordLastTransactionID();
         //Restore timelimit
         $this->Timelimit = $savetimelimit;
+
         return $result;
     }
 
@@ -663 +725 @@
      * This makes sure that client and server are in a known state.
      * Implements RFC 821: HELO <SP> <domain> <CRLF>
      * and RFC 2821 EHLO.
+     *
      * @param string $host The host name or IP to connect to
-     * @access public
-     * @return boolean
+     *
+     * @return bool
      */
     public function hello($host = '')
     {
         //Try extended hello first (RFC 2821)
-        return (boolean)($this->sendHello('EHLO', $host) or $this->sendHello('HELO', $host));
+        return $this->sendHello('EHLO', $host) or $this->sendHello('HELO', $host);
     }
 
     /**
      * Send an SMTP HELO or EHLO command.
-     * Low-level implementation used by hello()
-     * @see hello()
+     * Low-level implementation used by hello().
+     *
      * @param string $hello The HELO string
-     * @param string $host The hostname to say we are
-     * @access protected
-     * @return boolean
+     * @param string $host  The hostname to say we are
+     *
+     * @return bool
+     *
+     * @see    hello()
      */
     protected function sendHello($hello, $host)
     {
@@ -691 +756 @@
         } else {
             $this->server_caps = null;
         }
+
         return $noerror;
     }
 
     /**
      * Parse a reply to HELO/EHLO command to discover server extensions.
      * In case of HELO, the only parameter that can be discovered is a server name.
-     * @access protected
-     * @param string $type - 'HELO' or 'EHLO'
+     *
+     * @param string $type `HELO` or `EHLO`
      */
     protected function parseHelloFields($type)
     {
-        $this->server_caps = array();
+        $this->server_caps = [];
         $lines = explode("\n", $this->helo_rply);
 
         foreach ($lines as $n => $s) {
@@ -724 +790 @@
                             break;
                         case 'AUTH':
                             if (!is_array($fields)) {
-                                $fields = array();
+                                $fields = [];
                             }
                             break;
                         default:
@@ -742 +808 @@
      * $from. Returns true if successful or false otherwise. If True
      * the mail transaction is started and then one or more recipient
      * commands may be called followed by a data command.
-     * Implements rfc 821: MAIL <SP> FROM:<reverse-path> <CRLF>
+     * Implements RFC 821: MAIL <SP> FROM:<reverse-path> <CRLF>.
+     *
      * @param string $from Source address of this message
-     * @access public
-     * @return boolean
+     *
+     * @return bool
      */
     public function mail($from)
     {
         $useVerp = ($this->do_verp ? ' XVERP' : '');
+
         return $this->sendCommand(
             'MAIL FROM',
             'MAIL FROM:<' . $from . '>' . $useVerp,
@@ -760 +828 @@
     /**
      * Send an SMTP QUIT command.
      * Closes the socket if there is no error or the $close_on_error argument is true.
-     * Implements from rfc 821: QUIT <CRLF>
-     * @param boolean $close_on_error Should the connection close if an error occurs?
-     * @access public
-     * @return boolean
+     * Implements from RFC 821: QUIT <CRLF>.
+     *
+     * @param bool $close_on_error Should the connection close if an error occurs?
+     *
+     * @return bool
      */
     public function quit($close_on_error = true)
     {
@@ -773 +842 @@
             $this->close();
             $this->error = $err; //Restore any error from the quit command
         }
+
         return $noerror;
     }
 
@@ -780 +850 @@
      * Send an SMTP RCPT command.
      * Sets the TO argument to $toaddr.
      * Returns true if the recipient was accepted false if it was rejected.
-     * Implements from rfc 821: RCPT <SP> TO:<forward-path> <CRLF>
+     * Implements from RFC 821: RCPT <SP> TO:<forward-path> <CRLF>.
+     *
      * @param string $address The address the message is being sent to
-     * @access public
-     * @return boolean
+     *
+     * @return bool
      */
     public function recipient($address)
     {
         return $this->sendCommand(
             'RCPT TO',
             'RCPT TO:<' . $address . '>',
-            array(250, 251)
+            [250, 251]
         );
     }
 
     /**
      * Send an SMTP RSET command.
      * Abort any transaction that is currently in progress.
-     * Implements rfc 821: RSET <CRLF>
-     * @access public
-     * @return boolean True on success.
+     * Implements RFC 821: RSET <CRLF>.
+     *
+     * @return bool True on success
      */
     public function reset()
     {
@@ -808 +879 @@
 
     /**
      * Send a command to an SMTP server and check its return code.
-     * @param string $command The command name - not sent to the server
-     * @param string $commandstring The actual command to send
-     * @param integer|array $expect One or more expected integer success codes
-     * @access protected
-     * @return boolean True on success.
+     *
+     * @param string    $command       The command name - not sent to the server
+     * @param string    $commandstring The actual command to send
+     * @param int|array $expect        One or more expected integer success codes
+     *
+     * @return bool True on success
      */
     protected function sendCommand($command, $commandstring, $expect)
     {
         if (!$this->connected()) {
             $this->setError("Called $command without being connected");
+
             return false;
         }
         //Reject line breaks in all commands
         if (strpos($commandstring, "\n") !== false or strpos($commandstring, "\r") !== false) {
             $this->setError("Command '$command' contained line breaks");
+
             return false;
         }
-        $this->client_send($commandstring . self::CRLF);
+        $this->client_send($commandstring . static::LE, $command);
 
         $this->last_reply = $this->get_lines();
         // Fetch SMTP code and possible error code explanation
-        $matches = array();
-        if (preg_match("/^([0-9]{3})[ -](?:([0-9]\\.[0-9]\\.[0-9]) )?/", $this->last_reply, $matches)) {
+        $matches = [];
+        if (preg_match('/^([0-9]{3})[ -](?:([0-9]\\.[0-9]\\.[0-9]) )?/', $this->last_reply, $matches)) {
             $code = $matches[1];
             $code_ex = (count($matches) > 2 ? $matches[2] : null);
             // Cut off error code from each response line
             $detail = preg_replace(
                 "/{$code}[ -]" .
-                ($code_ex ? str_replace('.', '\\.', $code_ex) . ' ' : '') . "/m",
+                ($code_ex ? str_replace('.', '\\.', $code_ex) . ' ' : '') . '/m',
                 '',
                 $this->last_reply
             );
@@ -849 +923 @@
 
         $this->edebug('SERVER -> CLIENT: ' . $this->last_reply, self::DEBUG_SERVER);
 
-        if (!in_array($code, (array)$expect)) {
+        if (!in_array($code, (array) $expect)) {
             $this->setError(
                 "$command command failed",
                 $detail,
@@ -860 +934 @@
                 'SMTP ERROR: ' . $this->error['error'] . ': ' . $this->last_reply,
                 self::DEBUG_CLIENT
             );
+
             return false;
         }
 
         $this->setError('');
+
         return true;
     }
 
@@ -875 +951 @@
      * commands may be called followed by a data command. This command
      * will send the message to the users terminal if they are logged
      * in and send them an email.
-     * Implements rfc 821: SAML <SP> FROM:<reverse-path> <CRLF>
+     * Implements RFC 821: SAML <SP> FROM:<reverse-path> <CRLF>.
+     *
      * @param string $from The address the message is from
-     * @access public
-     * @return boolean
+     *
+     * @return bool
      */
     public function sendAndMail($from)
     {
@@ -887 +964 @@
 
     /**
      * Send an SMTP VRFY command.
+     *
      * @param string $name The name to verify
-     * @access public
-     * @return boolean
+     *
+     * @return bool
      */
     public function verify($name)
     {
-        return $this->sendCommand('VRFY', "VRFY $name", array(250, 251));
+        return $this->sendCommand('VRFY', "VRFY $name", [250, 251]);
     }
 
     /**
      * Send an SMTP NOOP command.
-     * Used to keep keep-alives alive, doesn't actually do anything
-     * @access public
-     * @return boolean
+     * Used to keep keep-alives alive, doesn't actually do anything.
+     *
+     * @return bool
      */
     public function noop()
     {
@@ -911 +989 @@
      * Send an SMTP TURN command.
      * This is an optional command for SMTP that this class does not support.
      * This method is here to make the RFC821 Definition complete for this class
-     * and _may_ be implemented in future
-     * Implements from rfc 821: TURN <CRLF>
-     * @access public
-     * @return boolean
+     * and _may_ be implemented in future.
+     * Implements from RFC 821: TURN <CRLF>.
+     *
+     * @return bool
      */
     public function turn()
     {
         $this->setError('The SMTP TURN command is not implemented');
         $this->edebug('SMTP NOTICE: ' . $this->error['error'], self::DEBUG_CLIENT);
+
         return false;
     }
 
     /**
      * Send raw data to the server.
-     * @param string $data The data to send
-     * @access public
-     * @return integer|boolean The number of bytes sent to the server or false on error
+     *
+     * @param string $data    The data to send
+     * @param string $command Optionally, the command this is part of, used only for controlling debug output
+     *
+     * @return int|bool The number of bytes sent to the server or false on error
      */
-    public function client_send($data)
+    public function client_send($data, $command = '')
     {
-        $this->edebug("CLIENT -> SERVER: $data", self::DEBUG_CLIENT);
-        set_error_handler(array($this, 'errorHandler'));
+        //If SMTP transcripts are left enabled, or debug output is posted online
+        //it can leak credentials, so hide credentials in all but lowest level
+        if (self::DEBUG_LOWLEVEL > $this->do_debug and
+            in_array($command, ['User & Password', 'Username', 'Password'], true)) {
+            $this->edebug('CLIENT -> SERVER: <credentials hidden>', self::DEBUG_CLIENT);
+        } else {
+            $this->edebug('CLIENT -> SERVER: ' . $data, self::DEBUG_CLIENT);
+        }
+        set_error_handler([$this, 'errorHandler']);
         $result = fwrite($this->smtp_conn, $data);
         restore_error_handler();
+
         return $result;
     }
 
     /**
      * Get the latest error.
-     * @access public
+     *
      * @return array
      */
     public function getError()
@@ -949 +1038 @@
     }
 
     /**
-     * Get SMTP extensions available on the server
-     * @access public
+     * Get SMTP extensions available on the server.
+     *
      * @return array|null
      */
     public function getServerExtList()
@@ -959 +1048 @@
     }
 
     /**
-     * A multipurpose method
-     * The method works in three ways, dependent on argument value and current state
-     *   1. HELO/EHLO was not sent - returns null and set up $this->error
-     *   2. HELO was sent
-     *     $name = 'HELO': returns server name
-     *     $name = 'EHLO': returns boolean false
-     *     $name = any string: returns null and set up $this->error
-     *   3. EHLO was sent
-     *     $name = 'HELO'|'EHLO': returns server name
-     *     $name = any string: if extension $name exists, returns boolean True
-     *       or its options. Otherwise returns boolean False
-     * In other words, one can use this method to detect 3 conditions:
-     *  - null returned: handshake was not or we don't know about ext (refer to $this->error)
-     *  - false returned: the requested feature exactly not exists
-     *  - positive value returned: the requested feature exists
+     * Get metadata about the SMTP server from its HELO/EHLO response.
+     * The method works in three ways, dependent on argument value and current state:
+     *   1. HELO/EHLO has not been sent - returns null and populates $this->error.
+     *   2. HELO has been sent -
+     *     $name == 'HELO': returns server name
+     *     $name == 'EHLO': returns boolean false
+     *     $name == any other string: returns null and populates $this->error
+     *   3. EHLO has been sent -
+     *     $name == 'HELO'|'EHLO': returns the server name
+     *     $name == any other string: if extension $name exists, returns True
+     *       or its options (e.g. AUTH mechanisms supported). Otherwise returns False.
+     *
      * @param string $name Name of SMTP extension or 'HELO'|'EHLO'
+     *
      * @return mixed
      */
     public function getServerExt($name)
     {
         if (!$this->server_caps) {
             $this->setError('No HELO/EHLO was sent');
-            return null;
+
+            return;
         }
 
-        // the tight logic knot ;)
         if (!array_key_exists($name, $this->server_caps)) {
-            if ($name == 'HELO') {
+            if ('HELO' == $name) {
                 return $this->server_caps['EHLO'];
             }
-            if ($name == 'EHLO' || array_key_exists('EHLO', $this->server_caps)) {
+            if ('EHLO' == $name || array_key_exists('EHLO', $this->server_caps)) {
                 return false;
             }
-            $this->setError('HELO handshake was used. Client knows nothing about server extensions');
-            return null;
+            $this->setError('HELO handshake was used; No information about server extensions available');
+
+            return;
         }
 
         return $this->server_caps[$name];
@@ -1001 +1089 @@
 
     /**
      * Get the last reply from the server.
-     * @access public
+     *
      * @return string
      */
     public function getLastReply()
@@ -1015 +1103 @@
      * With SMTP we can tell if we have more lines to read if the
      * 4th character is '-' symbol. If it is a space then we don't
      * need to read anything else.
-     * @access protected
+     *
      * @return string
      */
     protected function get_lines()
@@ -1030 +1118 @@
         if ($this->Timelimit > 0) {
             $endtime = time() + $this->Timelimit;
         }
-        while (is_resource($this->smtp_conn) && !feof($this->smtp_conn)) {
+        $selR = [$this->smtp_conn];
+        $selW = null;
+        while (is_resource($this->smtp_conn) and !feof($this->smtp_conn)) {
+            //Must pass vars in here as params are by reference
+            if (!stream_select($selR, $selW, $selW, $this->Timelimit)) {
+                $this->edebug(
+                    'SMTP -> get_lines(): timed-out (' . $this->Timeout . ' sec)',
+                    self::DEBUG_LOWLEVEL
+                );
+                break;
+            }
+            //Deliberate noise suppression - errors are handled afterwards
             $str = @fgets($this->smtp_conn, 515);
-            $this->edebug("SMTP -> get_lines(): \$data is \"$data\"", self::DEBUG_LOWLEVEL);
-            $this->edebug("SMTP -> get_lines(): \$str is  \"$str\"", self::DEBUG_LOWLEVEL);
+            $this->edebug('SMTP INBOUND: "' . trim($str) . '"', self::DEBUG_LOWLEVEL);
             $data .= $str;
             // If response is only 3 chars (not valid, but RFC5321 S4.2 says it must be handled),
             // or 4th character is a space, we are done reading, break the loop,
@@ -1060 +1158 @@
                 break;
             }
         }
+
         return $data;
     }
 
     /**
      * Enable or disable VERP address generation.
-     * @param boolean $enabled
+     *
+     * @param bool $enabled
      */
     public function setVerp($enabled = false)
     {
@@ -1074 +1174 @@
 
     /**
      * Get VERP address generation mode.
-     * @return boolean
+     *
+     * @return bool
      */
     public function getVerp()
     {
@@ -1083 +1184 @@
 
     /**
      * Set error messages and codes.
-     * @param string $message The error message
-     * @param string $detail Further detail on the error
-     * @param string $smtp_code An associated SMTP error code
+     *
+     * @param string $message      The error message
+     * @param string $detail       Further detail on the error
+     * @param string $smtp_code    An associated SMTP error code
      * @param string $smtp_code_ex Extended SMTP code
      */
     protected function setError($message, $detail = '', $smtp_code = '', $smtp_code_ex = '')
     {
-        $this->error = array(
+        $this->error = [
             'error' => $message,
             'detail' => $detail,
             'smtp_code' => $smtp_code,
-            'smtp_code_ex' => $smtp_code_ex
-        );
+            'smtp_code_ex' => $smtp_code_ex,
+        ];
     }
 
     /**
      * Set debug output method.
-     * @param string|callable $method The name of the mechanism to use for debugging output, or a callable to handle it.
+     *
+     * @param string|callable $method The name of the mechanism to use for debugging output, or a callable to handle it
      */
     public function setDebugOutput($method = 'echo')
     {
@@ -1109 +1212 @@
 
     /**
      * Get debug output method.
+     *
      * @return string
      */
     public function getDebugOutput()
@@ -1118 +1222 @@
 
     /**
      * Set debug output level.
-     * @param integer $level
+     *
+     * @param int $level
      */
     public function setDebugLevel($level = 0)
     {
@@ -1127 +1232 @@
 
     /**
      * Get debug output level.
-     * @return integer
+     *
+     * @return int
      */
     public function getDebugLevel()
     {
@@ -1136 +1242 @@
 
     /**
      * Set SMTP timeout.
-     * @param integer $timeout
+     *
+     * @param int $timeout The timeout duration in seconds
      */
     public function setTimeout($timeout = 0)
     {
@@ -1145 +1252 @@
 
     /**
      * Get SMTP timeout.
-     * @return integer
+     *
+     * @return int
      */
     public function getTimeout()
     {
@@ -1154 +1262 @@
 
     /**
      * Reports an error number and string.
-     * @param integer $errno The error number returned by PHP.
-     * @param string $errmsg The error message returned by PHP.
+     *
+     * @param int    $errno   The error number returned by PHP
+     * @param string $errmsg  The error message returned by PHP
      * @param string $errfile The file the error occurred in
-     * @param integer $errline The line number the error occurred on
+     * @param int    $errline The line number the error occurred on
      */
     protected function errorHandler($errno, $errmsg, $errfile = '', $errline = 0)
     {
         $notice = 'Connection failed.';
         $this->setError(
             $notice,
-            $errno,
-            $errmsg
+            $errmsg,
+            (string) $errno
         );
         $this->edebug(
-            $notice . ' Error #' . $errno . ': ' . $errmsg . " [$errfile line $errline]",
+            "$notice Error #$errno: $errmsg [$errfile line $errline]",
             self::DEBUG_CONNECTION
         );
     }
@@ -1179 +1288 @@
      * Relies on the host providing the ID in response to a DATA command.
      * If no reply has been received yet, it will return null.
      * If no pattern was matched, it will return false.
+     *
      * @return bool|null|string
      */
     protected function recordLastTransactionID()
@@ -1191 +1301 @@
             $this->last_smtp_transaction_id = false;
             foreach ($this->smtp_transaction_id_patterns as $smtp_transaction_id_pattern) {
                 if (preg_match($smtp_transaction_id_pattern, $reply, $matches)) {
-                    $this->last_smtp_transaction_id = $matches[1];
+                    $this->last_smtp_transaction_id = trim($matches[1]);
+                    break;
                 }
             }
         }
@@ -1203 +1314 @@
      * Get the queue/transaction ID of the last SMTP transaction
      * If no reply has been received yet, it will return null.
      * If no pattern was matched, it will return false.
+     *
      * @return bool|null|string
+     *
      * @see recordLastTransactionID()
      */
     public function getLastTransactionID()

src/wp-includes/pluggable.php

@@ -210 +210 @@
                 global $phpmailer;
 
                 // (Re)create it, if it's gone missing
-                if ( ! ( $phpmailer instanceof PHPMailer ) ) {
+                if ( ! ( $phpmailer instanceof PHPMailer\PHPMailer\PHPMailer ) ) {
                         require_once ABSPATH . WPINC . '/class-phpmailer.php';
                         require_once ABSPATH . WPINC . '/class-smtp.php';
-                        $phpmailer = new PHPMailer( true );
+                        $phpmailer = new PHPMailer\PHPMailer\PHPMailer( true );
                 }
 
                 // Headers

tests/phpunit/includes/mock-mailer.php

@@ -1 +1 @@
 <?php
 require_once( ABSPATH . '/wp-includes/class-phpmailer.php' );
 
-class MockPHPMailer extends PHPMailer {
+class MockPHPMailer extends PHPMailer\PHPMailer\PHPMailer {
         var $mock_sent = array();
 
         function preSend() {