Microsoft goes open source with Outlook PST format

by Bharat Suneja

It seems with each passing day Microsoft gets closer to offering an openly documented and interoperable platform. Working with Exchange for a number of years, many customers notice that Exchange Server is a remarkably well-documented product, not only in terms of the feature documentation but also its protocols such as Exchange ActiveSync and Messaging Application Programming Interface (MAPI). This documentation can be found in Exchange Server Protocols on MSDN. It’s no wonder Exchange ActiveSync is the leading mobile sync protocol licensed by many mobile device manufacturers and OEMs, including Apple, Google, Sony Ericson, and Nokia.

Earlier this week Microsoft announced release of documentation detailing the PST file format used by Microsoft Outlook. The documenation can be found at [MS-PST]: Outlook Personal Folders File Format (.pst) Structure Specification. Microsoft also released two new open source tools on CodePlex – the PST Data Structure View Tool (PSTViewTool), and PST File Format SDK. The documentation and open source tools will help Microsoft partners and developers create more interoperable solutions that can natively access, modify, index, search and archive data in PST files, without having Outlook installed. Cloud services may be able to offer tools to easily import PST files.

Exchange 2010 includes Personal Archives (aka Online Archive, or archive mailboxes) to allow users to store many years worth of messages on the server, eliminating the need for PST files. Microsoft also recommends moving away from PST files in order to protect messaging data (particularly on user laptops), meet the organization’s retention and compliance policies or applicable regulations, and to facilitate and lower costs of e-discovery. PST files are generally used by POP3/IMAP users. When using Outlook with Exchange Server, messages are stored in the mailbox on Exchange and not downloaded to a PST file (although a user can  create or modify an Outlook Profile to do this). In Cached Mode, Outlook uses an OST file to create a locally cached copy of your Exchange mailbox for offline access. Users work with the local copy, and Outlook syncs it with the mailbox when connected to Exchange. OST files also offer more security, and are tied to the Outlook profile and Exchange mailbox for which they’re created. For more about Outlook data files, see Introduction to Outlook data files.

{ 2 comments… read them below or add one }

Emily N. June 11, 2010 at 7:54 am

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Kevin A. June 16, 2010 at 12:17 pm


Wrong website for that question by far! Unless of course the author is feeling particularly charitable.


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