I am having critical problems with mail delivery.
For one thing users randomly get a NDR with the following message.
UNABLE TO DELIVER MESSAGE DUE TO COMMUNICATIONS FAILURE.
I noticed that this happens when there is one address in the TO field and it
also gets BCC to another.
The delivery is intended for internal and external recipients. Sometimes
the TO gets the error and sometimes the BCC.
The other issue is where a message is being sent to a recipient and CC to
others and the TO does not get it.
These are all internal mailboxes.
These users are all in different servers within the same site. But the
weird thins is that users that reside one the same server, some get it and
I have exchange 5.5 spk 4 on all servers.