SMTP Fallback for Delivery and Read Notification

[JM-Lemmi]

Checking "Receipt Notification" will successfully send the mail, but not trigger a delivery notification (probably a limitation of zimbra) and also return "undelivered mail returned to sender", even though the mail was actually sent.

Undelivered Mail returned to sender..zip

I propose to catch mail with this option and send it Over Fallback or reject, since the actually sent mail will not contain the delivery notification anymore

[JM-Lemmi]

RFC3464 Section 2: An Extensible Message Format for Delivery Status Notifications