We have been usin gthe Microsoft Intelligence Mail Filter that is incorporated in Exchange Service Pack 2 for a while now. Previous we had the gateway set at 8/10 and the store set at 3/10. Basically, this means that if an inbound email scores 8 or above (on the spam scale) then the gateway action takes effect. In our case this was set to reject.
Now over the years because our CIAOPS web site had our email address on the front page we attracted lots and lots and lots of spam. This is why it is never a good idea to put plain text email addresses on web sites. admittedly most of the spam that did get through was getting caught by the junk mail filter and ending up in the junk mail folder in Outlook, but there was just so much. So rather than try and sort through it all the best bet was to crank down the gateway setting.
So we changed our gateway setting on the IMF from 8 to 7 ( just a single point ) and we went from > 1,000 spam emails a day to less than 10! Amazing eh? Just goes to show you gotta keep on top of these settings overtime. The other good thing is that it does prove how well the Microsoft Intelligent Mail Filter (IMF) does work.