Microsoft will build anti-spam technology into its Exchange Server from the middle of next year, a move resellers of third-party software say could benefit the whole market.

The server module, called Microsoft Exchange Intelligent Message Filter, is similar to the anti-spam technology already built into Microsoft Outlook 2003 and Hotmail.

It uses a scanner which identifies spam by its content but also by its behaviour on the network. The spam filter will be updated monthly from spam lists sent in by Hotmail users.

Microsoft Exchange Intelligent Message Filter is designed to work with other third-party anti-spam products and has been backed by security players such as Brightmail.

Ross McWilliam, managing director of reseller Zen Software, said the move could make the market bigger.

"This can be a positive thing. The fact that Microsoft is coming into the market shows how serious the problem is. Companies that have been putting off buying an anti-spam solution will now be pushed to look at the options," he said.

But Graham Cluley, senior technology consultant at anti-virus and anti-spam vendor Sophos, questioned whether putting anti-spam software on the server was the right approach.

"Our resellers tell us large companies don't want this, and it may not work," he said.

"Exchange doesn't have the infrastructure to stop spam effectively for them. The job needs to be done closer to the internet access point, before it gets into the organisation. Also, deciding to update spam definitions on a monthly basis is too slow."

In 1999 Microsoft introduced SmartScreen, which checked for spam in users' Hotmail accounts. Initially the results were good, but spammers quickly learned how to bypass the controls.

Microsoft is also working on other anti-spam technology, including developing a 'Trusted Sender' programme with AOL, Yahoo and Earthlink. It has also put in lobbying time and funding to support anti-spam legislation in the US.

iain_thomson@vnu.co.uk