Allowed optional installation of swiftmailer 6 if plattform >= PHP 7. Submodule for swiftmailer not required as it is also a dependency within composer.

Author: thirsch

.gitmodules

@@ -1,7 +1,3 @@
-[submodule "lib/vendor/swiftmailer"]
-	path = lib/vendor/swiftmailer
-	url = https://github.com/swiftmailer/swiftmailer.git
-	branch = 5.x
 [submodule "lib/plugins/sfDoctrinePlugin/lib/vendor/doctrine"]
 	path = lib/plugins/sfDoctrinePlugin/lib/vendor/doctrine
 	url = https://github.com/LExpress/doctrine1.git

lib/mailer/sfMailer.class.php

@@ -239,10 +239,17 @@ public function setDeliveryAddress($address)
    */
   public function compose($from = null, $to = null, $subject = null, $body = null)
   {
-    return Swift_Message::newInstance()
+    $msg = null;
+
+    if(version_compare(Swift::VERSION, '6.0.0') >= 0) {
+      $msg = new Swift_Message($subject);
+    } else {
+      $msg = Swift_Message::newInstance($subject);
+    }
+
+    return $msg
       ->setFrom($from)
       ->setTo($to)
-      ->setSubject($subject)
       ->setBody($body)
     ;
   }
@@ -277,12 +284,12 @@ public function sendNextImmediately()
   /**
    * Sends the given message.
    *
-   * @param Swift_Transport $transport         A transport instance
+   * @param Swift_Message   $message         A transport instance
    * @param string[]        &$failedRecipients An array of failures by-reference
    *
    * @return int|false The number of sent emails
    */
-  public function send(Swift_Mime_Message $message, &$failedRecipients = null)
+  public function send(Swift_Message $message, &$failedRecipients = null)
   {
     if ($this->force)
     {