Submitted by Hans Salvisberg on Sat, 2007-04-07 16:44
Receiving incoming email and making it available to your users via POP3 or IMAP is only the first half of running a Message Transfer Agent (MTA). The other half is to relay outgoing email from your users to the world.
We don't want to run an open relay, of course, so we we need some form of authorization.
