One of my web design clients gets around 90,000 spam emails a month. We had a real problem trying to address to issue. Hours were being wasted filtering through the crap. Plus a lot of important emails were getting missed. We tried several email hosting service like Fastmail but they all failed to bring the spam down to a reasonable number. Eventually we tried Google Apps and changed all the email addresses. Now the spam is back under control with almost all but a few spam emails going into the Spam folder. I was so impressed that I wanted to try Postini for myself. I signed up and eventually after lots of messing about got it working. I've been using it for about 7 months now and its pretty damn good, aspecially for £6 a year per mailbox. If you have an issue with spam I would highly recommend you give it a go.