Or you can simply use Mozilla mail (former Netscape mail) which nicely handles as many mail accounts as you like, good spamfilter and all the other features you want. All in a free, addfree package. And to top it off it doesn't have barn-sized securityholes like Outlook/Outlook Express does. If you do not want to the full package that includes a Browser you can download the pure mailclient as well (Thunderbird).

Mozilla:
http://www.mozilla.org/
Thunderbird:
http://www.mozilla.org/products/thunderbird/

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