Index: program/steps/mail/sendmdn.inc
===================================================================
--- program/steps/mail/sendmdn.inc	(revision 2818f8e9ed5e8853e33636ac8efe09e2a4161618)
+++ program/steps/mail/sendmdn.inc	(revision 881217a5c95dbfe4e62154a2c0edd135b504220e)
@@ -20,4 +20,7 @@
 */
 
+// only process ajax requests
+if (!$OUTPUT->ajax_call)
+  return;
 
 if (!empty($_POST['_uid'])) {