My organization is considering using the Microsoft Exchange Intelligent Message Filter as our front-end spam filter, but we're still running Exchange 2000 Server. Can I install just one Exchange Server 2003 system to host the Exchange Intelligent Message Filter?

Exchange Intelligent Message Filter requires Exchange 2003 but doesn't require native Exchange 2003 mode. If you install it on an Exchange 2003 server and use that server as your SMTP bridgehead, the filter will function as a gateway spam filter. However, you won't be able to take full advantage of its capabilities.

In a native Exchange 2003 organization, Exchange Intelligent Message Filter implements two blocking levels, according to the spam confidence level (SCL) thresholds that you set. First, the filter drops messages that have an SCL higher than the specified gateway threshold; this level of action occurs regardless of the mode in which your organization runs.

Second, if you host mailboxes on an Exchange 2003 server, the filter processes messages that have an SCL lower than the gateway threshold but higher than the Store threshold and files those messages in users' junk mail folders. If your mailboxes aren't on an Exchange 2003 server, the filter simply delivers those messages to users' Inboxes. Be aware, too, that Exchange Intelligent Message Filter is available only to Exchange customers who are signed up for the Software Assurance (SA) program.