Today, based on feedback, we’ve lowered the timeout to 24 hours. In the future, we are planning more improvements, although we do not have any dates or details to share at this time. Thank you for the continued feedback.
An error occurred while saving the commentAnonymous commented
I've had this problem, too.
When my mail was sent, Exchange Online didn't check the other party's MX records, and tried to post it for 12 hours.
The equivalent of my users need to send 12 hours before they know that the mail sent failed!
It's really not being received!