Microsoft Has Published the Outlook PST Specification

Posted by Abel Avram on Feb 27, 2010

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Microsoft has published the Outlook PST file format specification in order to “facilitate interoperability and enable customers and vendors to access the data in .pst files on a variety of platforms” as promised in October last year.

Microsoft has been opening up for interoperability reasons across different platforms for a while, with one important move being the implementation of OASIS Open Document Format (ODF) version 1.1 in Office 2007 SP2 released in 2009. That implementation included Word, Excel and PowerPoint and it was documented as Microsoft Office File Formats. By doing this, Microsoft joined a number of other products implementing ODF such as OpenOffice.org/Sun StarOffice (which pioneered the format), IBM Lotus Symphony (which is based off of OpenOffice) and Google Docs.

Microsoft has not just implemented ODF in Office, but have also released a number of specifications regarding Windows, Exchange Server 2007, SharePoint Server 2007 and others, including:

• Protocol documentation for Windows client and Windows Server covered by the MCPP and WSPP licensing programs, made available pursuant to the Consent Decree and the European Commission's 2004 Decision, together with protocol documentation for Application Services and the .NET Framework.

• Protocol documentation for Office 2007, Exchange Server 2007 to Microsoft Outlook 2007, and Office SharePoint Server 2007.

• Format documentation for the Office Binary File formats.

• Documentation for certain Microsoft computer languages that are implemented by Microsoft products.

Microsoft announced the upcoming publication of Outlook PST file format last year. Developers have been able to access data in PST files through the Messaging API (MAPI) because the Outlook Object Model has been available since 2007, however Outlook had to be installed on the client machine for that to work. Now, not only is Outlook is no longer needed to access the PST files, but one can program against it on any platform, client or server, because the documentation offers complete details on how data is organized and stored.

The Outlook PST documentation has been released under Open Specification Promise, which allows “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.”

Microsoft said they are opening up PST to “enable some organizations to finally comply with new government policies for corporate governance, especially with regard to maintenance of interoffice communications.”

Microsoft made some proposals to the European Commission investigating its antitrust related practices promising to disclose information leading to improved interoperability with some Microsoft products including Exchange:

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 denied that publishing the PST file format specification had anything to do with the antitrust investigation, but it never explained what benefit it is trying to obtain by improving interoperability. The end result of this move is unclear because while some companies might use the PST format to develop applications for it, possibly even in the cloud, others might use it to migrate from existing Outlook to other solutions.