Microsoft uses Apache License for open source Outlook tools

CodePlex projects allow developers to more easily see Outlook PST data.

Microsoft has released two open source tools on CodePlex that let developers more easily create apps for Outlook PST files. Those tools are not only open source, they've been released under the Apache License (instead of one of Microsoft's own two open source licenses). The tools follow Microsoft's February release of full documentation for its Outlook 2010 .PST files.

The .PST documentation was released under Microsoft's Open Specification Promise, which means that developers can download and use the specification without contacting Microsoft or paying royalties. However, the specification itself included some funky, and questionable patent language that could apply to applications that ultimately tap into Outlook .PST files.

My impression is if you want to use the .PST files to write some custom software for your enterprise users, no sweat. If you want to build a commercial app, better get the intellectual property lawyers involved. (Of course, I'm a journalist, not a lawyer, so don't misconstrue my opinion as legal advice.)

It is important to note, too, that the Outlook .PST files themselves have not been released under Apache -- only the developer tools.

Specifically, these are a .PST Data Structure View Tool and a .PST File Format Software Development Kit (SDK). According to Microsoft:

  • The PST Data Structure View Tool ( is a graphical tool allowing the developers to browse the internal data structures of a PST file. The primary goal of this tool is to assist people who are learning .pst format and help them to better understand the documentation.
  • The PST File Format SDK ( is a cross platform C++ library for reading .pst files that can be incorporated into solutions that run on top of the .pst file format. The capability to write data to .pst files is part of the roadmap will be added to the SDK.

As of this writing, within a few hours of the Microsoft press release, the data structure tool already had a few hundred downloads and the SDK a few dozen.

Prior to the release of the technical documentation, a developer needed a copy of Outlook installed on the desktop and had to use the Messaging API (MAPI) or Outlook Object Model to use the data in Outlook's e-mail, calendar and attachments. So the documentation coupled with tools that let you use it is a step in the right direction.

There are other projects on CodePlex covered by the Apache license, or even the GPL, but many of these were not created by Microsoft employees. Still it is interesting how Microsoft-related open source projects are increasingly using open source licenses other than the ones created by Microsoft.

I, for one, am glad to see Microsoft begin to dabble with mainstream open source licenses. Makes me feel like there's hope that the company can convert its massive intellectual capabilities into better serving customers rather than bullying competitors.

Microsoft insists that opening its .PST 2010 data formats has nothing to do with pressure from the European Commission to do exactly that. But you be the judge because in July, the EC noted, as part of its press release regarding Web browser competition:

"In July 2009, Microsoft also made proposals in relation to disclosures of interoperability information that would improve interoperability between third party products and several Microsoft products, including Windows, Windows Server, Office, Exchange, and SharePoint (see MEMO/09/352 ). Microsoft is publishing improved proposals on its website. The Commission welcomes this initiative. Even though it remains informal vis-à-vis the Commission, Microsoft’s proposal, which is in the form of a public undertaking, includes warranties that Microsoft offers to third parties and that can be privately enforced."

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