The announcement came Tuesday in conjunction with the first upgrade to Exchange Server 2003, Microsoft's E-mail server platform.
At least one analyst hailed the news.
"When Microsoft originally announced IMF, it said it would only be available to SA customers. Just about everybody they talked to said that was crazy," said Peter Pawlak, lead analyst at Directions on Microsoft, a research firm that tracks Microsoft's moves.
Intelligent Message Filter, an add-on to Exchange Server 2003, is based on the SmartScreen anti-spam technology used by Microsoft's Hotmail service and integrated with Outlook 2003. By adding it to the server, said Pawlak, companies can create an additional layer of anti-spam filtering.
"IMF uses the same spam filtering that's in Outlook 2003 and puts it on the server so administrators can decide how aggressively they want to look at spam entering the network," said Pawlak. "Once it's delivered to the Outlook client, the user can set his own level to, for instance, filter even more aggressively."
IMF can assign a "spam confidence level" to messages based on the regularity of word associations, and "train" itself to better spot spam by monitoring what kind of messages users designate as junk mail. It also includes tools for archiving spam, rather than simply discarding it, so that administrators can review messages designated as spam to catch false positives.
The filtering technology also offers ways for third-party anti-spam vendors to hook their products into Exchange 2003.
"Microsoft heard from customers and analysts both," said Pawlak, "and realized that fighting spam was the most crucial problem they had to lick. It didn't make any sense for them to limit IMF's distribution."
The Intelligent Message Filter, which can be downloaded free of charge from Microsoft's Web site, requires Exchange Server 2003 Standard or Enterprise edition, something that sticks in Pawlak's craw.
"If they were really serious," about fighting spam, he said, "they'd come up with an IMF for Exchange 2000, or even Exchange 5.5. Because it only works with Exchange 2003, Microsoft's obviously trying to provide an incentive for people to upgrade."
Along with the IMF add-on, Microsoft has posted a deployment guide in Microsoft Word format that it urged all users to review before installing the new tool. "If you do not configure Intelligent Message Filter correctly, your messaging environment can be negatively affected," Microsoft said on its Web site.
Also on Tuesday, Microsoft released Service Pack 1 for Exchange 2003, which features, among bug fixes, a refreshed user interface for Outlook Mobile Access, updated migration tools for customers moving from Exchange 5.5, and enhanced migration support in a new Active Directory Connector.
"There are a few new features in SP1," said Pawlak, "but they're very small things. The majority of it is bug fixes."
Exchange Server 2003 Service Pack 1 can be downloaded free of charge from Microsoft's site, or ordered on CD for a $5 shipping and handling charge.