Mixmaster is is an anonymous remailer software, tt encrypts your email messages before sending them and routes the messages through a series of anonymous proxies, you can choose how many nodes and what proxies you want on the chain, blacklisting a particular remailer server if you don’t trust it, mixmaster also provides protection against traffic analysis by delaying the sending of the messages.
Mixmaster runs on *BSD, Linux and Microsoft Windows. If you have questions about remailers and Mixmaster one of the best points of calls is the newsgroup: alt.privacy.anon.server
You can read the mailing list for remailer operators, and subscribe, at: http://lists.mixmin.net/mailman/listinfo/remops
Mixmaster remailer software homepage: http://mixmaster.sourceforge.net/