Microsoft publishes Outlook PST files, but uses funky patent language

Microsoft had promised that patents would be would not be an issue, but then says its 'patents might cover your implementation.'

Microsoft today published the technical specifications for its Outlook 2010PST files. Microsoft had promised in October that it would do so.

Added 02/23 per comment below: The document can be found here.

Microsoft contends that it opened the specifications out of goodwill towards partners and customers who had been asking for it. I had previously blogged that I thought this had more to do with the promises Microsoft made to the European Commission in July 2009, when it said it would make "disclosures of interoperability information that would improve interoperability between third party products and several Microsoft products, including Windows, Windows Server, Office, Exchange, and SharePoint." The EC is fond of slapping Microsoft with enormous fines for anti-competitive behavior.

At the time that Microsoft said it would publish the PST file format and it promised, according to Paul Lorimer, group manager of Microsoft Office Interoperability in a blog post:

"When it is complete, it will be released under our Open Specification Promise, which will allow anyone to implement the .pst file format on any platform and in any tool, without concerns about patents, and without the need to contact Microsoft in any way."

I had concluded that Microsoft was making its Outlook 2010 open source, saying that if it the code was free to be seen and was also free to be used by anyone, under any circumstance, without concern over patents, that's open source. I was contacted by Microsoft and told that I was wrong -- although Microsoft was publishing the documentation, it was not making the PST files open source.

I stand corrected. This is not open source. The first thing Microsoft does in the documentation is to spell out a rather confusing set of Intellectual Property rights to anyone using this specification. I've read many a TechNet and MSDN document and I've never seen one that begins with:

Patents. Microsoft has patents that may cover your implementations of the technologies described in the Open Specifications. Neither this notice nor Microsoft's delivery of the documentation grants any licenses under those or any other Microsoft patents. However, a given Open Specification may be covered by Microsoft's Open Specification Promise (available here: or the Community Promise (available here: If you would prefer a written license, or if the technologies described in the Open Specifications are not covered by the Open Specifications Promise or Community Promise, as applicable, patent licenses are available by contacting"

Does this jive with the promise made in October that, it will be released under our Open Specification Promise, which will allow anyone to implement the .pst file format on any platform and in any tool, without concerns about patents, and without the need to contact Microsoft in any way."

I've e-mailed Microsoft to ask and if I receive a reply, I will post it.

UPDATED 02/24/10: I asked Microsoft PR to answer the above question. I wanted an explanation of how a developer can use the specification without concern about infringing on patents when Microsoft is also stating that any particular implementation may infringe on one of Microsoft's many patents not covered by its open specification promise and that its promise would therefore not cover it. I asked for an example of a kind of implementation that could be considered infringing.

I didn't get a straight answer -- and I didn't really expect to. I believe the technologists at Microsoft are truthfully trying to make their products more interoperable (whatever the impetus), but the business folks and lawyers have mucked it up and complicated it, so that Microsoft can always sue at a later date, claiming patent infringement, if it chooses to.

Essentially, the answer was, it is up to the individual to read through all the documents and understand them, or to negotiate a license with Microsoft if it chooses to.

However, Microsoft did make it clear that using the .PST specification itself is safe. I think the gist is that any other technology you may be using in conjunction with PST might not be.

Here is the exact text of Microsoft's official reply:

"As indicated, Microsoft has published the Outlook Personal Folders File Format (.pst) Structure Specification under the Microsoft Open Specification Promise (OSP).  The OSP terms can be found at The OSP is one means by which Microsoft shares its technology around the world for use by others to build innovative and interoperable solutions. It assures developers and customers that they are free to implement specifications without paying fees or royalties, regardless of platform.

The license terms for the .pst specification are included in the specification text. (The “Patents” language you highlighted is part of a general intellectual property rights notice with links to the OSP, the Microsoft Community Promise, and Microsoft’s licensing group, so that the licensing terms applicable to a particular specification can be confirmed.) The OSP page also includes an FAQ section."

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