Some are better than others.
http://www.google.com/search?hl=en&lr=&q=spam+blockers&btnG=Search
my mother uses ICX and is getting an ungodly amount of SPAM. I use MSN that employs the junk mail feature, so I really don't have to deal with or know much about blocking Spam. I figure there has to be a download of some kind, .... right?
Seth

Chowhound
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GameSpot
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TechRepublic