Mail flow doesn't work if Exchange 2007 Installed on Server 2008 with certain routers

Windows vista and windows Server 2008 have the TCP autotuning setting enabled by default, so if the router is small or outdated maybe it doesn't support that feature, so we have to disable the feature on Server 2008 to make that work, but beware that this will decrease the server performance

Symptom:
Mail flow doesn't work if Exchange 2007 Installed on Server 2008 with certain small routers


Cause:
That's if the router doesn't support TCP autotuning settings in Windows Server 2008.

Resolution:
open RUN==CMD== and type this command

netsh interface tcp set global autotuninglevel=disabled

this will disable the feature and we back in business

here is more info about parameters for that command from MS sites:


The following autotuning settings are available if a router supports TcpWindowScaling:

Disabled: Fix the receive window at its default value.

Highly Restricted: Allow the receive window to grow beyond its default value, but do so very conservatively.

Restricted: Allow the receive window to grow beyond its default value, but limit such growth in some scenarios.

Normal: Allow the receive window to grow to accommodate most scenarios.

Experimental: Allow the receive window to grow to accommodate extreme scenarios.