The Internet Engineering Task Force (IETF) has turned down Microsoft's technical contribution to the Sender ID proposal.

A combination of Microsoft's Caller ID and a domain authentication scheme devised by Meng Wong, co-founder of email forwarding and hosting company Pobox.com, Sender ID is designed to cut spam by identifying where an email has come from.

But Microsoft's proposals have already met with opposition from the open source community, which is unhappy about the software giant's licensing terms. Both the Apache Software Foundation and Debian have said that they would not deploy the scheme.

Microsoft's patents also troubled the IETF group considering the proposals.

Andrew Newton, co-chair of the IETF working group reviewing Sender ID, said in an email to other members: "There is at least rough consensus that the participants of the working group cannot accurately describe the specific claims of the patent application.

"We do feel that future changes regarding the patent claim or its associated licence could significantly change the consensus of the working group, and at such a time it would be appropriate to consider new work of this type."

The IETF will continue to evaluate the technology. And Microsoft has stated that it still has support from key industry players.

"AOL, Cloudmark, IronPort, VeriSign, Bell Canada and the 54-member Email Service Provider Coalition have voiced support for the Sender ID licence offered by Microsoft," said the company in a statement.

"There's broad support for Sender ID technology and we encourage others to support and implement this technology so that together we can do more to tackle spam."