Exchange Connectiontimeout

You need to change the connectiontimeout parameter in Exchange if you keep getting "421 4.4.1 Connection timed out" SMTP errors. This error message means that Exchange closed the SMTP connection while POPcon or the sender host of the Email is still transmitting and not finished.

Normally this is not severe because POPcon will just continue to transfer the rest of the emails in the next mail cycle.

The cause of this problem is the default ConnectionTimeout parameter of Exchange receive connectors. By default this timeout is set to 10 Minutes maximum length of any given SMTP session.

You can use this Exchange management shell command to set a longer SMTP connection timeout:

Set-ReceiveConnector "*default*" -ConnectionTimeout 01:00:00

Instead of the "*default*" name please use the name of the active receive connector (not always the Default* one). If you are not sure you can just repeat this command with the name of each of the receive connectors (See SERVER configuration > Hub transport > receive connectors).

Please restart the "Microsoft Exchange Transport" service after executing the shell commands. We've had feedback from two customers that the changes to the timeout only went active after a restart of the transport service in their systems.