I get about 3000 spam emails per day. That's not an exageration. I have tried IHateSpam and MailWasher and AVG anti-spam, and all of them were pretty good, but I found it actually took less time to simply let all the spam come in and delete them from my server by hand, using a webmail interface, than it took to go through the spam folder and dig out emails I wanted to get, after they'd been sorted by IHateSpam, Mailwasher or AVG.
Then I heard about Cloudmark and tried it. I have been using Cloudmark for about a week and can tell you it is the best of them all. It does not mark as spam anything that isn't actually spam. So far out of 13,000 spams I've checked in the spam folder in the last 4 days, it has not put one email into the spam category that did not belong there.
I'm not affiliated with Cloudmark, and I don't usually rave about Microsoft products. But Cloudmark is an exceptional product and deserves many accolades. It has reduced my time spent handling spam from about an hour a day to about 3 minutes.