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.