We have a few Groups in the AD, and in the group members there a few email addresses, that are point to an external domain. These messages are not delivered:
I am deeply sorry, but I was not able to deliver your mail to the following
email@example.com : #5.1.0 Address rejected.
This is a permanent delivery failure. The delivery has been tried 0 times
and will not be rescheduled again.
What am I missing?