I've recently installed Drupal 6, and was having problems sending out emails (specifically for new users and password resets).
The problem was that sometimes the mail was coming through, and other times it wasn't (it didn't even appear in our mail server logs).
After lots of scouting around, I noticed that in /var/log/maillog (on FC6), the relay kept on changing.
On our network, we have 3 domain controllers, one of which is a mail server. Send mail was using it's "Smart" relay to figure out w...