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we are running sbs2008 with exchange 2007. One user suddenly can't receive emails from one external sender any more and the sender never gets a return email. That user has to use hotmail or gmail etc to send to that sender.

I am thinking must be blocked in somewhere but could not find it. Any direction can point me to? Thanks.

Update 1:

With Exchange Troubleshooting Assistant, I track down all mails sent from that sender, have been marked spams in the subject:

***SPAM***

I guess the spam then be deleted by server quietly?? I will need to check spam settings and come back later. Thanks.

Update 2:

I found in Anti-Spam -> Content Filter: If the message contains "SPAM", will be blocked.

Option1: Is it a good practice to have this kind of setting here? because no one is acknowledged about this deletion. On the other side, if I remove this policy, I may get hundreds of SPAM in our Inbox. Option2: How do I define a while list, so mails from certain sender will not be marked as SPAM?

Update 3:

OK - I am totally cool now. I am using this GUI tool to manage the whilelist for anti-spam: http://gsexdev.blogspot.com/2009/02/content-filtering-system-whitelist-gui.html

Thanks guys.

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2 Answers

Check to see if they are on a blacklist: http://www.mxtoolbox.com/blacklists.aspx

Then does the sender have a PTR records? If not, they should since they could have problems sending to many domains.

Can the user e-mail other people in your domain? If so, then it is likely his computer somehow.

You will probably have to work with their IT provider as you really need to attack this problem from the sender's side and trace the e-mail. It may have nothing to do with your server, but could be blocked before it even leaves their systems for some reason.

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They are not on the blacklist. They can't email to any other people in our domain. Their emails can reach my hotmail/gmail etc email boxes. –  starchx May 25 '11 at 6:24
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It could be that you've exceeded the named properties limit. The answers to this question have some good trouble shooting tips as well.

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Thanks for the tips. I then use the tracking tool to track down all the emails sent from them has been marked: "Spam" prefix. What to do now? –  starchx May 25 '11 at 6:25
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