I use fetchmail in daemon mode and have procmail set up to filter my email through bogofilter (http://bogofilter.sourceforge.net/). As for outgoing mail postfix, exim, and sendmail are popular. From my laptop I do use a python script to cache mail my mail when I'm not connected. I then use a script which sends my email over ssh to my work computer which uses sendmail to send it all out. I discuss those scripts at http://miyu.idolstarastronomer.com:8080/cgi-bin/cgiwrap/devries/blosxom.cgi/2004/04/27#laptop-mail and they are written in python.
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