If you have a LAN linux server, or are willing to build and set one up, make a gateway with spamassassin (or any other filtering program) and have it do fetchmail on all your accounts. Not only will you filiter spam, but you can also add in a virus checker if you like, and you can access your mail via imap on the server directly so you could access it from multiple workstations. Got a setup like that at home, it's great. The initial setup can be a pain though, email is not the simplest protocols. (well pop/imap is not bad, it's SMTP that can get complicated)