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Windows Server 2003 Rejecting IMAP connections

Posted on 2011-03-17
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Last Modified: 2012-05-11
I'm a new member of a small software company, and since I have basic networking knowledge (CCENT), I am the go-to individual for anything relating to network problems (which often don't have anything to do with network problems).  

Our Windows Server 2003 is rejecting IMAP connections when the originate from outside the network.  More specifically, if the server is referred to by its public name imapserver.domain.com, the connections are rejected.  However any connections referring to its local name imapserver.domain.local or 10.10.10.41 (its static ip), resolve without problem.  I have checked router logs, and the router shows that the connections are accepted, but using netcat, I can see the connections are being immediately refused.  However, a netstat dump shows that the server is listening on port 143 (IMAP port) (as it should be given it accepts local connections).  

My knowledge of networking is minimal, but this doesn't seem to be a network problem (i.e. a router configuration/permissions problem).  I would guess it's some sort of permissions setting on our IMAP server that got changed.  That said, I have almost 0 knowledge of Windows server 2003 (or any version for that matter), so please be clear with your advice/questions.  

Thanks for any help

NOTE: We were under an FTP attack earlier in the day, and a visiting friend of the company tried to fix it.  Besides entering a blanket deny all into the router for incoming FTP connections, I have no idea what he did.  This may not be relevant, but its the reason people started poking around.  

NOTE: I'm still in college (work a few hours a week for the company currently), which is why I get contacted with these issues, but always after someone else (who knows less than I) pokes around first.  This doesn't always end well.  
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Question by:hgetson
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Hypercat (Deb) earned 1000 total points
ID: 35168256
It's not a problem on the Windows server, since it works internally.  If there was something on the server blocking that port, you wouldn't be able to get to it internally either.  It's most likely that something got changed/deleted from the router while the "visiting friend" was fixing the other problem.

You would need to be sure that the IMAP port (TCP/UDP 143) is not blocked by the router and further that the router is forwarding incoming packets on that port to the private IP address of the server.  What kind of router do you have? If you post the make/model it's possible that I or someone else here may be able to help you check this and fix it if that is the problem.
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Author Closing Comment

by:hgetson
ID: 35173710
I had been checking the firewall rules carefully, but I had overlooked a few of the port forwarding rules had been lost (including the IMAP rule).  Thanks for forcing me to recheck them all again.
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