Just spent some time working on reconfiguration of one of the SMTP servers I run. The odd thing was that even the tests that should fail went through without a hitch. So I dug into the logs a bit further and found no record of any of the messages I was sending, either good or bad. So I looked at the headers and it appears the ISP for the hotel is doing NAT port redirection of all outbound connections on port 25. It's a practice that is convenient for guests but may pose both an opening for spammers to stop by and use the connection as well as annoyance for people who don't like third parties unwittingly intercepting their mail.
by Joshua Brauer on September 6, 2004