Question : Incoming mail from a domain is refused

Exchange Server 2003

550 5.7.1 Requested action not take: message refused

Taken from the log:
216.82.244.35 - mail54.messagelabs.com [23/Jul/2007:09:44:50 -0800] "HELO -? mail54.messagelabs.com SMTP" 250 45
216.82.244.35 - mail54.messagelabs.com [23/Jul/2007:09:44:50 -0800] "MAIL -? FROM:on.com> SMTP" 250 51
216.82.244.35 - mail54.messagelabs.com [23/Jul/2007:09:44:50 -0800] "RCPT -? TO:.com> SMTP" 250 0
216.82.244.35 - mail54.messagelabs.com [23/Jul/2007:09:44:53 -0800] "QUIT -?mail54.messagelabs.com SMTP" 240 101

Answer : Incoming mail from a domain is refused

>>Actually it did make it to the exchange server, the log above came from my SMTP log.

Making it to the exchange server, and making it to exchange are two totally separate things.

Just because it is in the SMTP logs, doesn't mean exchange saw it - if you have AV on it that has blocked it for whatever reason, it can show up in the SMTP logs but not message tracking.

As opposed to searching on the recipient - search based on time and search through looking for the email.  If you find it, you will have more details - if not, well then we are back to AV and Anti-Spam.  If it is not in the spam or virus logs, then what is it logging?  Is it in the ACCEPTED logs?  Can you enable those logs?