For those who have made the jump to Exchange 2003, you now can take advantage of IMF from Microsoft. This is an add-in program that runs on your Exchange 2003 server and uses Microsoft SmartScreen technology to reject or flag spam. The setup is very simple and the options are limited but adequate.
This is a welcomed add-on for Exchange 2003, which also includes RBL support. RBLs can be effective at cutting down the amount of spam, however they tend to be a little too aggressive at times, and block legitimate email.
There are two options for setting up IMF. These options are organization wide so they must be set carefully.
The first is Gateway Blocking Configuration. This setting allows you to choose what Spam Confidence Level (SCL) you want to block at the gateway and how you want to block it (Archive/Delete/No Action/Reject). The second option is the Store Junk email configuration. This option asks to you to select a SCL that would trigger the email to be moved to a users Junk Mail folder if they are using Outlook 2003.
How is the SCL determined? This is with Microsoft's patented SmartScreen technology. This technology looks for patterns in email that may seem spam-like (spam-o-rific) and gives it a rating depending on how spam-o-rific it looks.
More information about IMF can be found here, including the installation documentation and installation media.
http://www.microsoft.com/exchange/downloads/2003/imf/default.asp
- Joel