Technical details for those operating UofT services follows:

408 messages sent via appsmtp or devsmtp between March 2 00:24:52 and 09:30:00 were delayed until after 09:30:00. Many institution services use appsmtp. Another 668 messages were dropped when there were issues sending the message, and were having problems with the bounceback message.

In each such case, we are trying to send a notification saying that their message failed to deliver. If the “envelope-from address” is incorrect, then the sender can't be notified per email standards.