Microsoft is now offering its Sender ID email authentication specification under its Open Specification Promise (OSP) program, the company said today.

OSP is basically a guarantee from Microsoft that the technology is available to developers, ISPs, and users for free, without licensing restrictions and fees.

Richi Jennings, an analyst with Ferris Research, says this means Microsoft is confirming that it won't take action to protect its patents and other intellectual property associated with Sender ID, namely its Purported Responsible Address (PRA), which is patented. Concerns about PRA's licensing derailed its adoption as an IETF standard two years ago, although Sender ID remains an IETF RFC.

Sender ID is Microsoft's protocol for verifying that an email came from the Internet domain it says it came from. It checks the sending server's IP address to prevent the spread of malware, spam, and phishing emails.

But the protocol has met with some resistance by developers worried about licensing as well as technology problems. "Few developers chose to implement the extra features of Sender ID that distinguish it from SPF [Sender Policy Framework], most notably the PRA algorithm," Jennings explains. "This was because of a combination of [intellectual property] licensing worries and some concerns that PRA could generate more false positives than SPF alone."

Jennings says today's announcement is merely Microsoft's formalizing the OSP program. "[Microsoft] made similar promises back in 2004 -- it's just reiterating the promises today."

Microsoft has acknowledged concerns about its licensing terms. In a Q&A on its Website, it said putting Sender ID under the OSP umbrella will help "promote further industry interoperability among all commercial software solutions that use email authentication, including open source solutions, by making Sender ID more clearly available to the entire Internet ecosystem."

There are over 600 million users worldwide of Sender ID, according to Microsoft. Some 36 percent of all legitimate email sent worldwide is Sender ID-compliant, and around 5.5 million domains, according to the company, which says adoption of Sender ID by the Fortune 500 has jumped from 7 percent a year ago to over 23 percent today.

"Sender authentication technologies like Sender ID are important tools that help ensure email security, and by making Sender ID available under OSP, Microsoft is addressing the interoperability needs of heterogeneous email infrastructures," Eric Allman, chief science officer at Sendmail, said in a statement.

— Kelly Jackson Higgins, Senior Editor, Dark Reading