Microsoft Exchange Server 2003 SP2 - 6.5.7638
Last week when we tried to email anyone from a certain domain with a small attachment it wouldn't send. We could email them without
attachments, but not with. People from other domains could email them with the same attachment though. At the time our domain was on & off being blacklisted due to a Zeus bot virus. Today we can email them with an attachment.
The error we got back from our Exchange server was:
Final-Recipient: RFC822; email@example.com
Action: failed Status: 5.5.0
X-Supplementary-Info: <our-server.our-domain.com #5.5.0 smtp;550 Requested action not taken: mailbox unavailable>
Googling this error has not proved fruitful for me. Although it seems likely it was due to being black listed, it doesn't explain why we could email them without attachments at the time.
Anyone got any ideas? I'm paranoid this will reoccur and I want to be ahead of the game if it does.