I use SpamArrest.com.
Its an easy challenge/response system based on the senders email address. ONLY human beings can self-authorize, and I can also manually pre-authorize senders as well. The best part is NO (that means NONE) spam comes into my machine, it stays on the Spamarrest server for me to review at my leisure. By sorting on the subject line, I can spot genuine emails quickly and authorize those senders, all the rest I delete. Once a sender's address is authorized, all future email from them sails right through. This is better than any spam filter on a computer because 1) you still have to wait for it to load (and I'm getting about 1200 emails a day, at least 1150 are spam), 2) you still have to review the rejects for false postives, 3) some spam will still get through.
Its only costs $35/year (they have a free "lite" version), and has its own webmail reader for when I travel (with no ads) from any browser (even in Cozumel). It works with any current email client - it checks your email server every few minutes, and puts all your mail on their server. When you check for email, you're checking their server. Piece of cake to set up, very reliable, and I've had no complaints from models, clients, ebay customers, friends, etc.
Andy Pearlman Studio