spamtrainer was written to assist mail services administrators in updating and maintaining their SpamAssassin bayes database. When run, it will read the designated HAM and SPAM mailboxes, update the SpamAssassin databases and delete mail that has been learned from.
SpeedMail is a speedup Mail.app.
SweetMail is an e-mail program that supports multiple accounts and threading.
(shareware) ThinkArch allows you to archive MS Entourage email messages in DEVONThink Pro.
UTF-8 Output support for Pine
A small patch to enable UTF-8 output in Pine.
Webmailer is a program (actually a preference pane) for Mac OS X which lets you set it to open any URL or run any shell script, complete with the parameters lifted from the mailto link.