> > Err..... I know that postfix can bounce mail after it's recived.... I > > would be amazed if the other MTAs you mention cannot. > [ sendmail and Exim ] > > The problem with accept-then-bounce is that the message ends up stuck on > the *receiving* server. This is NOT a good way to handle email- > especially considering quite a bit of spam doesn't have a valid return > address of ANY kind ANYWHERE in the message, and viruses may technically > have a valid return address... but not a *correct* one. > > On high-load mail systems (ie, multi-million messages/day/server), this > can mean a LOT of dead-end messages stuck in the queue for days on end. > Unless you are proposing to move all spam/virus/malware checks into the MTA to be used during incomming SMTP sessions, this is a problem you are always going to have. There is nothing stoppping the MTA from checking the headers and bouncing during a SMTP session (though it does require a peek in the headers), but unlike SPF it isn't required.
Nick
