Every year, one of my good friends, Al, spends the summer at Frost Valley, a camp in the Catskills. Al is, generally, a very connected guy (technologically-speaking, that is; not in the organized crime sense). As a result, Al usually has issues with the firewall at the camp filtering IP traffic for services that he uses - SMTP, FTP, etc. Today, while trying to help troubleshoot an SMTP-filtering problem, I became aware of the fact that port 587 is an alternate port for SMTP, in additon to the stanard port 25. I found this very interesting because I had never heard this before.
I found an article in PC Magazine that states the following:
"But there is another SMTP submission port, port 587, which almost all mail server supports. In fact, according to the relevant standard, port 587 is the preferred port for mail submission. But even if the mail server software supports it, it may or may not be turned on. You need to check with the administrator or hosting service. Not all large hosting services support port 587."
It then goes on to talk about how to configure your mail client to point to port 587 for SMTP, rather than port 25. Hmm....
Maybe my knowledge of mail servers is a bit provincial, having always worked in academic IT departments, but I'm not aware of any mail servers that I have used that accept mail on 587. A quick attempt to telnet to 587 on one of our boxes yeilded no results.
If you've had any success using port 587, I would love to hear about it in the comments!