Exchange 2003 SMTP Hangs From Too Many Connections
Your Exchange 2003 server stops receiving messages
The SMTP service is still running
You telnet to port 25 (from the server – telnet localhost 25) and get this banner:
service not available, closing transmission channel
You open Exchange System Manager and drill down to view the Current Connections on your SMTP virtual server. It shows hundreds of connections that have been open for many days (measured in seconds).
If you have a secondary MX record that forwards all mail to your Exchange Server, the majority of the open connections are from that secondary server.
You are running the Intelligent Message Filter (IMF) features of Exchange 2003.
You need to restart the SMTP service. It will probably hang and you will need to kill it.
That is only a temporary fix, as the connections will continue to pile up.
The SMTP service fails to drop old connections due to a bug with the Sender ID Filter. If you disable that filter on your SMTP virtual server, the problem goes away.