If you want to be able to do anything you can imagine with your mail, just try the bat!... http://www.ritlabs.com/the_bat/
its loaded with features... you can filter on any possible aspect, and do anything (start programs, send auto-generated emails etc, even running an full mailinglist including controlling on certain keywords etc etc). I like the feature to filter incoming mails based on the category in your adressbook the sender is in (is this good english? I wonder...) -> I mean, I have several folders in my account like friends and study, and in my adressbook I have similar (not the same) folders in which my contacts are listed. And the bat filters accordingly to these category's -> emails from fellow students are punt in the folder students etc - and this way it works automatically, if I add someone to my adressbook in the categorie friends, all his mails are punt in the mailmap friends! damn easy if you get loads of mail.... (and I dont delete mails, save them, I have thousands of mails in the several folders - but its easy to search them with powerfull searchoptions)
I've used it for years, and it works under linux using wine. and the bat is the most important reason for me not to start using linux (althoug I hate m$ and winBlows) because I just cant find an email client soo good... and the option to use it with wine (tried it) well I dont like that...
so if anyone knows an emailclient for linux wich can dream of being as featurerich as the bat!, tell me plz!
grtz