Ignored when type 'multipart/mixed'

Author: rajpraiyalan

src/MailTracker.php

@@ -126,6 +126,7 @@ protected function createTrackers($message)
 //                $original_content = $message->getBody();
 
                 if ($message->getContentType() === 'text/html' ||
+                    $message->getContentType() === 'multipart/mixed' ||
                     ($message->getContentType() === 'multipart/alternative' && $message->getBody())
                 ) {
                     $message->setBody($this->addTrackers($message->getBody(), $hash));