50 is a lot. You might want to check Thunderbird as well. Like Greg says it will get through your email server but Thunderbird will filter it to a junk bin. It uses a bayesian filter (meaning as you mark things as spam it will learn).

Here's a pretty good article on spam filtering by Leo Laporte - http://techguylabs.com/radio/Main/StopSpam?action=browse

There are some server side spam filtering services as well. Some require a challenge/response method (not real fond of this), some intercept the mail, apply rules, and allow them to go through, and others require you to change your email address (using their servers where the software resides). All are valid ways to get rid of spam, however once your email address is out, well, there is not a lot that you can do.

I have one email address that is pretty much 99% spam now. Mostly this comes from having links on other websites (including this one). You may have noticed that I am using a hotmail address here. Its actually one of the better anti-spam mailboxes around. They do a pretty good job filtering it out.