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SMTP connection timeouts on Exchange 2003 server.

Posted on 2009-02-13
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Last Modified: 2012-05-06
We are having a problem with our Exchange 2003 server where sometimes e-mails will not be received.  The sender does not get any bounced messages, the message just disappears.  We have disabled or removed antispam, antivirus, and turned off all filtering in Exchange.  The SMTP logfile still shows:

0 EHLO 250 0 SMTP -
0 MAIL 250 0 SMTP -
0 RCPT 250 0 SMTP -
0 TIMEOUT 121 1075732556 SMTP -

For many of the connections.  Any ideas on this?

Thank you
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Question by:OAC Technology
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by:Mestha
ID: 23636901
What is between the server and the internet? Firewall of some kind?

-M
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Expert Comment

by:flyingsky
ID: 23636938
which one of the following do you mean?
1. Internal users cannot receive emails coming from outside
2. Internal users cannot receive emails coming from other internal users
3. Outside reciepient cannot receive email from internal users
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Author Comment

by:OAC Technology
ID: 23636956
Internal users cannot receive SOME e-mail from outside.  It seems random.  Outside recipients will always receive e-mail from the internal users.

There is a DSL modem/firewall between the server and the internet.
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by:flyingsky
ID: 23636970
check to see if you have multiple MX records for your domain
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Expert Comment

by:briandunkle
ID: 23636999
When you say it seems random, are you saying that specific outside users may get through one time but not another? (rather than, say, the same outside people being blocked consistently, but it being random which users those are)
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by:OAC Technology
ID: 23637005
Only one mx record is set
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by:OAC Technology
ID: 23637053
It seems to be they may get through one time but not another.  Although, the timeouts seem to be happening for comcast.net's connections pretty constantly.
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by:Mestha
ID: 23638085
Really need to be more precise with what is between the internet and the server, as some firewalls have SMTP scanning features which can cause this kind of problem.

-M
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Author Comment

by:OAC Technology
ID: 23638425
It's an Actiontek M1000 from Qwest.  The firewall is turned off on this modem.  That's the only thing between the internet and the server.
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by:Press2Esc
ID: 23653934
"Internal users cannot receive SOME e-mail from outside.  It seems random.  Outside recipients will always receive e-mail from the internal users."
Seems to be more a POP issue than SMTP...  Also, the IPs of the undelivered email may be being blocked or blacklisted - have your checked??  Any specific NDR or associated email header would be helpful....  P2E
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OAC Technology earned 0 total points
ID: 23654248
It turns out that I needed to change the MTU settings on the server to 1400.  Apparently since there was no router between the modem and the server, the server's MTU settings were too high for that DSL connection.  Once this was done, the connections all went through successfully and instantly.
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by:Press2Esc
ID: 23660541
Excellent DD.....  I am curious, what was the failing MTU value - 1500??
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by:OAC Technology
ID: 23660602
Yes, it was set to 1500 before
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by:Press2Esc
ID: 23699899
I suspected you'd say 1500 because of the DSL overhead, 1492 is the highest packet size DSL is able to handle...
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