Action: failed Status: 5.5.0

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; name@receivers-domain.net
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>
X-Display-Name: name@receivers-domain.net

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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.
fred2k3Asked:
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Simon Butler (Sembee)Connect With a Mentor ConsultantCommented:
While it is your server generating the NDR, the problem has come from the other side. Ultimately they were blocking your traffic and whatever tool they are using doesn't return any useful information.

Not a lot you can do about it unfortunately, as the remote server isn't under your control.
You can take measures to limit the impact of a future infection, such as giving Exchange its own dedicated IP address, dropping the use of Exchange 2003 (which is end of life later this month), consider using a third party filtering service so your email doesn't come from your IP address etc.

Simon.
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fred2k3Author Commented:
Ok thank you for the advice.
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