After some help diagnosing why Exchange 2010 Enterprise stops responding to SMTP events.
I can't find a pattern to it. It doesn't appear to be an actual timeout, as the server responds immediately with the error. To reproduce it I telnet into the server on port 25 and issue a EHLO. The server immediately replies with the 421:
421 4.4.1 Connection timed out
Once this starts happening I've found restarting the exchange box is the only reliable way to get it flowing again. Sometimes restarting the Transport service or the mailbox attendant service seems to fix it, but this could be coincidental as it often has no effect.
Best Answer
thanks Michael did some research could be related to resource usage, have added some extra memory to teh VM will see if it fixes it. here is a link with some info for anyone else having the same issue http://technet.microsoft.com/en-us/library/bb201658.aspx