MailMonitor

MailMonitor is a program enabling you to monitor incoming and outgoing mail traffic to and from you mail server and clients.

It tracks, displays and logs incoming and outgoing SMTP sessions, POP sessions and sent and received e-mails. It can store incoming and outgoing e-mail in a separate directory independent of mail clients. Finally, it keeps a trace of all e-mail related session traffic (at packet level). This enables you to explore in depth what is going on in your e-mail environment.
These features make MailMonitor a valuable tool for tracking your e-mail flow in your e-mail environment in case of problems with sending or receiving e-mail. Watch for unsolicited mail forwarding, SMTP hacking (spammers that use your server to send their messages) and a host of other e-mail server related problems.
Features:
View SMTP and POP3 sessions with complete session trace.
Track all e-mails passing your server.
Monitor SMTP authentication with IP, username and password.
Monitor POP authentication.
Scan for mail errors and abnormalities.
Store every e-mail passing your server.
See a complete packet level trace of e-mail traffic only.
Supports VPN tunnels.
Bottom line: If you have mail server problems, MailMonitor shows you what's going on at port and packet level.