The Internet Engineering Task Force (IETF) has provisionally rejected Sender ID, a proposed anti-spam specification from Microsoft, because of a possible intellectual property rights conflict.

On Saturday, the co-chair of an IETF working group called MARID (MTA Authorization Records in DNS), which is discussing how to ensure that the sender of a message is using an authentic address, said the working group's members had reached a rough consensus that Microsoft's specification should not be made a mandatory part of MARID's eventual standard.

At issue is the company's perceived lack of clarity over intellectual property conflicts - specifically, the company has said that it has applied for patents which could affect Sender ID, but has declined to give details. According to co-chair Andrew Newton's summary of votes by working group members, this possible conflict could not be ignored. "The working group has at least rough consensus that the patent claims should not be ignored," Newton wrote.

Newton stated that since Microsoft's patent application isn't publicly available, and working group members cannot accurately describe what its claims might be, MARID's co-chairs decided not to take a risk. "It is the opinion of the co-chairs that MARID should not undertake work on alternate algorithms reasonably thought to be covered by the patent application," Newton wrote.

He added, however, that should Microsoft change its position on the matter things could change. "Future changes regarding the patent claim or its associated license 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," he wrote.

Earlier, the Debian operating system project and the Apache server project said they would not implement Sender ID under its current licensing terms, arguing they are incompatible with open-source licenses.

The licensing dispute marks a serious setback for the Sender ID specification, designed to combat spam by authenticating the source of email messages. Sender ID combines Caller ID for E-mail, proposed by Microsoft, and Sender Policy Framework (SPF), proposed by Meng Wong, the founder of email service provider While many believe the project could make a significant dent in spam, open-source critics said Microsoft's licensing plans would disrupt the normal distribution of open-source software.

Microsoft has offered a royalty-free licence to anyone wishing to implement Sender ID in their products. The main problem with this, according to an analysis by Larry Rosen, general counsel of the Open Source Initiative, is that open source licences are treated as sublicensable. "Open source licenses contemplate that anyone who receives the software under license may himself or herself become a contributor or distributor.

"Software freedom is inherited by downstream sublicensees," Rosen wrote in the analysis, which was cited in Apache's statement last week. "Meanwhile, the Microsoft Sender ID patent licence continues the convenient fiction that there are 'End Users' who receive limited rights. That is unacceptable in open source licenses."

Like other critics, Apache's developers said they were concerned the specification was being pushed ahead without serious attention being paid to intellectual property risks, particularly the existence of Microsoft's pending Sender ID-related patents. "We feel that dismissal of unspecified, pending, patent claims recklessly shifts the risk and potential burden onto implementors," Apache said.

In his analysis, Rosen argued that under current conditions, if a developer wished to rebrand or redistribute an open source product supporting Sender ID it would have to contact Microsoft directly, which "gives Microsoft information about its competitors' plans that it has no reason to know".

Some open-source leaders have found Microsoft's terms acceptable. Open Source Initiative president Eric Raymond approved of the licence because it requires no royalty payment and may not even require licensees to sign an agreement.

David Anderson, chief executive of Sendmail, agreed with this assessment, and his company has released a Sendmail mail filter supporting Sender ID under its own open-source licence. Anderson said Sendmail had no plans to sign a licence agreement, and didn't see why any other users or developers would need to do so.

The original SPF proposal is not covered by possible Microsoft patents, industry observers noted, which could clear the way for its use in a standard.