Microsoft is throwing the full weight of Hotmail behind its Sender ID email authentication technology. It’s sidelining all incoming mail when it fails to pass a Sender ID check.

The software maker has begun warning Hotmail users with an on-screen alert when the sender of an incoming email cannot be verified using its Sender ID Framework. Mail that fails to pass the test will be placed in a junk mail folder or even deleted.

Microsoft is pushing Sender ID as a system for identifying and thwarting unwanted email. The technology works by verifying that emails originate from the domain from which they claim to have been sent. It checks the sending server's address against a registered list of servers that the domain owner has authorised.

By making all messages received by Hotmail go through the Sender ID check, Microsoft is not only making a strong play for the technology but also pushing ISPs and other businesses to publish their sender policy framework (SPF) records so that their mail does not get quashed.

Hotmail reserves the right to delete mail based on antispam and antiphishing heuristics and on the sender's reputation.

Organisations should publish their SPF records to "protect their domain and ultimately enhance their brand name," said an MSN spokeperson.

Microsoft is not the only major player promoting an antispam technology. Yahoo has an authentication service called DomainKeys, and IBM has rolled out an antispam system called FairUCE (fair use of unsolicited commercial email).

Yahoo licences out DomainKeys, and recently said it is working with Cisco to combine their antispam technologies and create an authentication system. IBM is promoting its technology with developers, saying it wants to help them build more effective antispam filters.

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