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Outlook Flooded with Undeliverable Emails

Posted on 2015-02-10
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Last Modified: 2016-06-03
Have a real strange problem here folks...

Environment is SBS 2010 with WIN7 clients, running Office 2010. There are 8 people in this environment and they all seem fine but one person who keeps getting undeliverable bounce backs on his outlook client, they all seem to come from the same domain, always with a barracuda error message. Here's the trick however, I have tested and re-tested their domain against blacklists and they are clean as a whistle, send an Email to myself on both my hotmail account and my exchange account (hosted on the cloud by intermedia) and they came through just fine. So it almost looks like outlook is just generating these bounce backs without even trying to send the Emails? Very strange...
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Question by:Marvio_Santos
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by:Gareth Gudger
ID: 40601556
I assume this means the user actually send to this domain originally and is getting rejected? If so, can you post the NDR here?

If they never sent to this domain this is likely just a backscatter attack. More info on a backscatter attack here. If it is, not much you can do except get a really good message-hygiene solution that can protect against this, or, blacklist that domain.
http://en.wikipedia.org/wiki/Backscatter_(email)
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Marvio_Santos earned 0 total points
ID: 40601646
I finally figured it out... They did have a virus infection a while back, but exchange was still trying to send the Emails from back when, cleared out all the queues and it was fine
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by:Gareth Gudger
ID: 40601732
Glad you got it going. That must have sent out thousands of emails to still be processing, even now. Did you get blacklisted?
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