I know Daniel is fairly familiar with Exim but I know nothing about these alternative MTAs. Can anyone provide sage advice on which has more features, is easier to configure, has powerful plugins, db support, IMAP server integration, virtual domains, spam filtering that sort of thing.
I'm not particularly familiar with postfix, but it seems to be "about the same" as exim, although when I did use it, it wasn't quite as flexible I'd definitely use exim 4.5 or later, because of integrated exiscan support as Craig has already mentioned. With postfix you can use amavisd for spam/virus scanning Both exim and postfix have support for db and ldap lookups. These allow for relatively free-form queries, which don't tie you to any particular schema. I seem to remember postfix enforced a particular LDAP schema, which was possible to change but rather tedious. I'm willing to be corrected on this point though :). Exim doesn't care. With database lookups you get virtual domains. IMAP server integration is trivial - courier uses "normal" maildir, which exim and postfix should be able to deliver to fine. Cyrus doesn't use normal maildir, but will accept incoming mails via LMTP, which both exim and postfix support. You can also deliver via a 'deliver' program, but it just accepts mail on stdin and delivers to cyrus via LMTP anyway. Both cyrus and courier do virtual domains, and both are reasonably good about it now. Cyrus supports a full-text index if you enable the squat process (which uses about the same amount of space as your mailspool, so don't enable it unless you have lots of space) WAND has some copies of the Exim book left over from NZNOG. I'd highly recommend this book, although it does only cover version 4.0, and there's been a lot of change since 4.50. It's a great start though.