Exchange 2003 on 2003 Ent.
Users are getting intermittent delays sending to two distinct , specific domains.
I can see their messages in the outbound queue just sitting there marked as retry or queued.
Selecting the domain shows only that "An SMTP Error has occured" with no other information.
Every other domain seems to have no problem.
The issues surfaced two weeks ago and lasted for a few days and then went away again.
Not all messages are being delayed.
How do I troubleshoot this ?