"Addressbook2pine is a utility that allows you to sync your OS X address book with pine's and alpine's addressbook." Handy.

"...a new open-source mail client for Mac OS X. Correo blends technology from two popular Mozilla projects, Camino and Thunderbird, to create a polished native Macintosh application."

"If you do a "get info" (Command-i) on any mailbox in Tiger's version of Mail, an Account Info window appears. From there you can do all sorts of useful things..."

The spam filtering in Apple Mail is bloody rubbish, so I'm giving this a go.

Plugin for Mail.app