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Microsoft introduced TCP/IP Auto tuning with Vista and Windows 2008 server. Its also a part of Windows 7 and 2008 R2.  This feature resizes IP packets which can  improve network performance.  Older network devices, however, like Cisco PIX firewalls do not support Auto tuning and can cause connection issues.


I had a client that was getting email undeliverable errors from a certain domain while successfully sending to various others.  After investigating OBL listings and various other possible culprits, the tech for the problematic domain  suggested looking at this.  My client has an Exchange 2007 environment installed on Windows 2008 SP2 servers.  Sure enough after disabling this feature on all the hub transport servers, the SMTP traffic was no longer timing out to this domain and mail flow was established.


To disable TCP/IP Auto Tuning, run the following from an elevated command prompt:


netsh interface tcp set global autotuning=disabled


For more information on TCP/IP Auto Tuning, Visit:

Posted on Friday, August 20, 2010 1:56 AM Windows 2008 Server , MS Exchange 2007 , MS Exchange 2010 | Back to top

Comments on this post: Windows 2008, Exchange, and TCP/IP Auto Tuning

# re: Windows 2008, Exchange, and TCP/IP Auto Tuning
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FANTASTIC POST. I had been banging my head on this for over a week. Had queue working great but and a few others just "hung" in queue. After about 10 hours this weekend I was narrowing it down to something with our PIX and/or 2008R2, but what? I was reading to have to upgrade PIX firewall firmware, but I googled this this morning. With feature on telnet to 25 would simply hang for ever, turned it off and banner back in a couple seconds. THANK YOU.
Left by Tom Robbins on Mar 12, 2012 11:27 AM

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