I use a commercial hosting service which includes email. It provides as options SpamAssassin and Spamdyke, which work as well as can be expected. Spamdyke's graylisting does a nice job of keeping out much spam, more effectively than anything else.

The hosting provider provides a web interface in addition to IMAP, but I use IMAP clients, primarily Thunderbird, rather than web interfaces to email.

What the provider does not have, and I'd very much like to have, is IMAP augmented by Sieve.