We're just beginning a migration from Exchange Server 5.5 to Exchange Server 2003. Can we start using the Microsoft Exchange Intelligent Message Filter (IMF) now?

As long as you have at least one Exchange 2003 server in your existing Exchange 5.5 organization, you can install IMF on that server and use it as your inbound SMTP bridgehead. You can use the Exchange 2003 Exchange System Manager (ESM) to configure IMF's gateway spam confidence level (SCL), but you won't be able to take advantage of IMF's store SCL until your migration is complete. Still, you'll probably find that IMF does a good enough job of filtering spam to make it worth deploying even without its store-filtering functionality. For more information about deploying IMF, see "Deploying Exchange Intelligent Message Filter," September 2004, InstantDoc ID 43151 and the Web-exclusive article "The Exchange Intelligent Message Filter," June 2004, InstantDoc ID 42682.