Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 19652)
+++ wp-includes/pluggable.php	(working copy)
@@ -216,6 +216,9 @@
 		$phpmailer = new PHPMailer( true );
 	}
 
+	// Set X-Mailer as WordPress, can be overridden later
+	$phpmailer->XMailer = 'WordPress ' . get_bloginfo( 'version' );
+
 	// Headers
 	if ( empty( $headers ) ) {
 		$headers = array();
@@ -285,6 +288,14 @@
 					case 'bcc':
 						$bcc = array_merge( (array) $bcc, explode( ',', $content ) );
 						break;
+					// add next 3 cases for ticket 19549
+					case 'xmailer': //PHPMailer variable name
+					case 'x-mailer': //Email header name
+						$phpmailer->XMailer = $content;
+						break;
+					case 'x-priority':
+						$phpmailer->Priority = $content;
+						break;
 					default:
 						// Add it to our grand headers array
 						$headers[trim( $name )] = trim( $content );