I wrote earlier in the year of my migration from Sendmail to QMail – and have never looked back. I am happily blocking a multitude of IP addresses and blocks, and in conjunction with SpamAssassin have vastly reduced the amount of spam I and my clients have to wrestle with.
My situtation is slightly different from that of web host, as outside of my research work I remotely manage web and other servers for clients (i.e. numerous servers for unrelated companies generally on their own premises or data centers). Outside of a handful among them running Lotus Domino or Microsoft Exchange servers using native SMTP, the majority have migrated to QMail as their MTA.
The configuration for my own servers and those of some of my clients is a package that includes POP and SMTP – using QMail, vpopmail, QmailAdmin, spamassassin and some more.
I particularly like the ease of blocking IPs in Qmail, however, I wanted to end the year with some links to well written how-to’s for the most popular MTAs.
Postfix – http://www.postfix.org/spam.html
Qmail – http://www.chrishardie.com/tech/qmail/qmail-antispam.html
Sendmail – http://www.sendmail.org/m4/anti_spam.html