Ticket #28039: 28039-test.php

<?php

require 'wp-load.php';

require_once ABSPATH . WPINC . '/class-phpmailer.php';

class PrintPHPMailer extends PHPMailer {
        /**
         * Override send() so mail isn't actually sent.
         */
        function send() {
                try {
                        if ( ! $this->preSend() ) {
                                return false;
                        }

                        echo $this->getSentMIMEMessage();

                        return true;
                } catch ( phpmailerException $e ) {
                        return false;
                }
        }
}

$phpmailer = new PrintPHPMailer( true );

add_action( 'phpmailer_init', function( $mailer ) {
        $mailer->AltBody = 'Wörld';
        $mailer->Encoding = 'quoted-printable';
} );

wp_mail(
        get_site_option( 'admin_email' ),
        'Hello',
        '<p><strong>Wörld</strong></p>',
        array(
                'Content-Type: text/html',
                sprintf( 'From: %s', get_site_option( 'admin_email' ) )
        )
);