Most email servers will tell you what kind they are as part of the SMTP protocol.
Netcraft runs a popular survey site where it shows statistics of web server platforms.
It would be cool to see the same thing for email servers.
Even if the server doesn't tell you what software it is, you can use features in nmap to analyze the packets and see what os/program produced them.-- lawpoop, Aug 08 2003 Netcraft Survey http://news.netcraft.com/Find out what software the most popular web servers a running. [lawpoop, Oct 04 2004] Nmap port scanner http://www.insecure...ap/versionscan.htmlNmap now features version scanning. [lawpoop, Oct 04 2004] SMTP Server Survey (Apr 2003) http://www.halfbake...p Netcat and MySQL.http://www.credentia.cc/surveys/smtp/latest/ [quanta, Oct 04 2004] My take on this was that someone _must_ already be doing this, I'm surprised Netcraft themselves doesn't. But a quick google didn't turn anything up.-- krelnik, Aug 08 2003 [krelnik] Yeah, believe it or not, I actually looked up this idea before I posted it. Didn't find anything either.-- lawpoop, Aug 08 2003 I nice idea, although technically a bit trickier than what netcraft does, because quite a lot of mail servers don't let on what they are. (+) though, 'cause it would interesting to know.-- neilp, Aug 08 2003 I was reading that the newest version of nmap can make guesses from datagram profiles of what program sent them. But I don't have any personal experience with it.-- lawpoop, Aug 08 2003 That nmap feature is mostly to guess what operating system is running, that doesn't necessarily tell you anything about what SMTP server is running.
Another thing that could get in the way of this are SMTP proxies. Cisco's PIX firewall has a feature called "Mail Guard" that optionally will blank out the contents of the banner that SMTP shows on startup, making it more difficult to identify the server.-- krelnik, Aug 08 2003 Nmap now features version scanning. So you can find out what mail server a site is running, depending on how well nmap implements version scanning.-- lawpoop, Sep 16 2003 random, halfbakery