--- smtp.module	2008-07-12 17:49:26.000000000 +0200
+++ smtp.module	2008-09-03 00:38:39.171875000 +0200
@@ -235,7 +235,7 @@ function _drupal_mail_wrapper($mailkey, 
             if (strpos($lvalue, 'text/html') !== FALSE) {
                $mail->IsHTML(TRUE);
             }
-            else if ((strpos($lvalue, 'multipart/mixed') !== FALSE) || (strpos($lvalue, 'multipart/alternative') !== FALSE)) {
+            else if ((strpos($lvalue, 'multipart/mixed') !== FALSE) || (strpos($lvalue, 'multipart/alternative') !== FALSE) || (strpos($lvalue, 'multipart/related') !== FALSE)) {
                //$body passed to smtp should already be formatted. add multipart header and tell phpmailer to leave it alone
                $mail->AddCustomHeader($key . ": " . $value);
                $mail->message_type = "pre";