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Exchange 2007 becomes spam machine when enabling smarthost

Posted on 2011-02-25
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Last Modified: 2012-05-11
OK....here's one for the grownups.

We have a client that's signed up for the mx-logic anti-spam service. Part of their account is outbound filtering and requires the installation of a smarthost. No problem.

The problem is that when I enable the smarthost and disable the normal send connector the server starts sending out buckets of spam.

Malware bytes didn't come up with anything on the server, spybot search and destroy didn't come up with anything. The server isn't a relay but like clockwork, we change the send connector and it starts spamming. Message log
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Question by:taiell0
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markdmac earned 500 total points
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Sounds like you are allowing all workstations that authenticate to relay. You most likely have one or more workstations that are infected and are sending spam out via outlook.
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by:davorin
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In addition to previous post:
How do you have smtp receive conectors configured?
You can set TLS encryption for client receive connector, so exchange will receive mails from SMTP clients on LAN over 587 port instead of port 25. In this way you should block sending from infected computers.
You can test open relay at www.mxtoolbox.com
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by:Alan Hardisty
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Check your network with something like Wireshark to see if you have a machine sending out spam via port 25 to the server.

Check to see if you are an open relay on www.checkor.com

Alan
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