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SMTP port to remote Exchange Server is blocked

Posted on 2010-11-19
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Last Modified: 2012-05-10
We've been having issues receiving email from a specific Exchange server to our Exchange server.  Neither server has problems sending to any other server, so this appears isolated.  

One thing I noticed is that when running telnet mail.remotedomain.org 25, it does not show any banner.  When running netstat it shows SYN_Sent from our server to theirs, but never completes the handshake.  From another location, I can telnet ok to the mail.remotedomain.org server just fine.

What might be causing this problem?  I can only imagine it is being blocked by the firewall or the IP is being denied by Exchange.  I don't have access to the server unfortunately.  Anyone have any ideas on what might be causing this?
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Question by:B1izzard
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LVL 15

Expert Comment

by:getzjd
ID: 34175053
Are you sure the other server is actually an exchange server and not a spam appliance or filtering device?
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LVL 31

Expert Comment

by:MegaNuk3
ID: 34175061
Have you pinged the server from both locations to see if the same IP address is returned?
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LVL 76

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by:Alan Hardisty
ID: 34175070
Does it show No banner at all or something like:

220 ***************************************************************************
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LVL 15

Expert Comment

by:getzjd
ID: 34175075
If it were blocked by the firewall specifically, then you should not even be making any type of initial connection.
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by:MegaNuk3
ID: 34175102
Pinger = pinged
Stupid iPhone autospell...
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LVL 76

Expert Comment

by:Alan Hardisty
ID: 34175115
Consider it corrected : )
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Author Comment

by:B1izzard
ID: 34175215
Here is the banner from a know good location:
220 remotedomain.org Microsoft ESMTP MAIL Service, Version: 6.0.3790.3959 ready at  Fri
, 19 Nov 2010 10:14:51 -0800

When telnetting from the problem location to the remote server, it gives:
Connecting To mail.remotedomain.org...Could not open connection to the host, on port 25
: Connect failed

The same IP is returned in both locations, so DNS is not an issue.

I can't think of anything other than the firewall blocking, or Exchange blocking by ip.  Anyone think any differently?
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Expert Comment

by:Alan Hardisty
ID: 34175228
It does sound like they are blocking you.

Can you test from another location or would you like one of us to test for you?
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Accepted Solution

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Alan Hardisty earned 250 total points
ID: 34175349
This is what I see:

220 domain.org Microsoft ESMTP MAIL Service, Version: 6.0.3790.3959 ready at  Fri
, 19 Nov 2010 10:39:55 -0800

That says to me that they are blocking you specifically.  Time to talk to their IT department.
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Assisted Solution

by:getzjd
getzjd earned 250 total points
ID: 34175351
Yes, sounds like you are being manually blocked then.  This is the information we needed to see.
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Author Closing Comment

by:B1izzard
ID: 34278182
Thanks.
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