Microsoft's recommendation for troubleshooting SMTP and POP on
an Exchange Server is to use protocol logs. However, logging can
waste time and disk space as the logs accumulate. If you send a
test message, you must go through all your logged email messages
to find the message. In addition, opening the message is often
time-consuming.  An alternative method I use for monitoring my
Exchange server is to open Exchange System Manager (ESM) and
navigate to the server that hosts the SMTP virtual server. Then,
I highlight Current Sessions and hold down the F5 key. SMTP and
POP connections display in the right-hand window.