How to Debug/Monitor SMTP Communications?

Question

Debug HTTP is easy, you have all sort of tools to do it (like Fiddler). What about SMTP?

How to Debug SMTP Communications?

My target system is Windows.

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Suggested tools:

• Ethereal
• tcpdump
• Microsoft Network Monitor

Answer 1

Try Ethereal - its a free network protocol analyzer.

The SMTP protocol is all ascii, so once you see whats inside the TCP connection, you should be good to go.

It will take a bit of work learning how to use Ethereal.

Answer 2

Use tools like ethereal (www.ethereal.com) or tcpdump (www.tcpdump.org), if you want to see the SMTP traffic.

If you like to check your server for compliance with relaying standards, do a

telnet relay-test.mail-abuse.org

from your SMTP server and it checks your server for relaying vulnerabilities.

Answer 3

You can use a SMTP development server, like Neptune or Antix. Both work the same way: they create a "fake" SMTP server in your machine so you can test your e-mail sending methods, without actually sending the messages they receive.

Answer 4

For the two people who responded with Ethereal: We renamed the project to Wireshark (http://www.wireshark.org) back in 2006 due to trademark issues. I strongly recommend upgrading.

Depending on your exact issue, Wireshark's Follow TCP Stream feature is pretty useful for debugging Internet Message protocols, including SMTP.