i use postini for spam filtering for my company and my hosted e-mail customers. postini acts as a proxy (you set them as your MX records, they forward legitima

i use postini for spam filtering for my company and my hosted e-mail customers. postini acts as a proxy (you set them as your MX records, they forward legitimate mail to your SMTP server, and users can view their quarantined queues on postini's website). unfortunately, they were bought by google some years back and the false-positive rates for even medium-level filtering have gone up quite a bit, so you have to constantly check your quarantine looking for legitimate mail. i wish there were more choices in the outsourced spam filtering market.