Mailinglist Archive

[I thought this was interesting from both a results and data gathering
methodology perspective.  -  jjk]

Fingerprinting the World's Mail Servers
by Ken Simpson and Stas Bekman
01/05/2007 

This summer, the sales staff at MailChannels came to the dev team with
an urgent request: "Can you tell us which companies are running
Sendmail? If we could know that, it would be so much easier to sell our
Sendmail-compatible product."

For those of us who understand the SMTP protocol, the answer was, of
course, a resounding "Yes." Most mail servers announce their identity
when you connect to them on TCP port 25. The dev team decided that this
was a summer science project they just had to get on top of. We even
gave the science project a name: PingedIn, and we hope to provide more
dynamic content on our skeletal website.

http://www.oreillynet.com/pub/a/sysadmin/2007/01/05/fingerprinting-mail-servers.html