I have an Exchange 2007 in place, the queue is giving me a 421 4.4.2. connection dropped error on some domains I’m sending to, tracing the logs shows the connection is dropped after the BDAT command.
I have found this on the internet:
BDAT is part of ESMTP protocol – while Ex2007 supports ESMTP, it does not support BDAT due to vulnerabilities that would crash smtp server (back in Exchange 2000 days). You can see all the ESMTP commands Exchange 2007 supports by telnet to the box and execute EHLO. While only very small number of domains still use BDAT, it is not necessary to make any changes to Exchange 2007.
If you want to fix this problem, you have to disable ESMTP on Exchange. To do this, issue this command:
Set-SendConnector -Identity <name of your send connector> -ForceHELO $true
