diff --git a/lib/classes/Swift/FileSpool.php b/lib/classes/Swift/FileSpool.php
index 4951b7b2a..780a3db13 100644
--- a/lib/classes/Swift/FileSpool.php
+++ b/lib/classes/Swift/FileSpool.php
@@ -207,9 +207,9 @@ protected function getRandomString($count = null)
         // This string MUST stay FS safe, avoid special chars.
         $base = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_-';
         $ret = '';
-        $strlen = strlen($base) - 1;
+        $strlen = strlen($base);
         for ($i = 0; $i < $count; ++$i) {
-            $ret .= $base[(int)mt_rand(0, $strlen)];
+            $ret .= $base[(int)mt_rand(0, $strlen - 1)];
         }
 
         return $ret;
diff --git a/lib/classes/Swift/Transport/MailTransport.php b/lib/classes/Swift/Transport/MailTransport.php
index b47d78fac..1825b62f8 100644
--- a/lib/classes/Swift/Transport/MailTransport.php
+++ b/lib/classes/Swift/Transport/MailTransport.php
@@ -218,12 +218,10 @@ public function send(Swift_Mime_Message $message, &$failedRecipients = null)
                 $this->_eventDispatcher->dispatchEvent($evt, 'sendPerformed');
             }
 
-            $message->generateId();  // Make sure a new Message ID is used
-
             $count = 0;
         }
 
-        //$message->generateId();  // Make sure a new Message ID is used
+        $message->generateId();  // Make sure a new Message ID is used
 
         return $count;
     }
diff --git a/lib/classes/Swift/Transport/SendmailTransport.php b/lib/classes/Swift/Transport/SendmailTransport.php
index 7143a1196..6afb9fc0a 100644
--- a/lib/classes/Swift/Transport/SendmailTransport.php
+++ b/lib/classes/Swift/Transport/SendmailTransport.php
@@ -145,11 +145,6 @@ public function send(Swift_Mime_Message $message, &$failedRecipients = null)
                 $this->_eventDispatcher->dispatchEvent($evt, 'sendPerformed');
             }
 
-            // TODO: Why do we need this only for the parameter "-f"?
-            // -> take a look at "AbstractSmtpTransport"
-            //
-            $message->generateId(); // Make sure a new Message ID is used
-
         } elseif (false !== strpos($command, ' -bs')) {
             $count = parent::send($message, $failedRecipients);
         } else {
@@ -161,7 +156,7 @@ public function send(Swift_Mime_Message $message, &$failedRecipients = null)
             );
         }
 
-        //$message->generateId(); // Make sure a new Message ID is used
+        $message->generateId(); // Make sure a new Message ID is used
 
         return $count;
     }