The Story of the Personal Storage Table Format (.PST)

Microsoft Outlook

Recent days, the news about “Microsoft to Open up Outlook .pst Format” is widely reported or speculated. As the background, at October 26, 2009, Paul Lorimer, Group Manager from Microsoft Office Interoperability, had announced that Microsoft will release documentation for the .pst file format in the first half of 2010 under the Open Specification Promise license, which allows programmers to interoperate with the .PST files in server and client conditions. In this post, I will give some introductions to the Personal Storage Table Format (.PST).

What’s Personal Storage Table Format (.PST)

A Personal Storage Table (or Personal Folders file) is the data file used to store all your messages, calendar events, and other items in Microsoft Outlook and other Microsoft software (Exchange Client, Windows Messaging).

Microsoft Outlook PST File

PST format is mostly used in home users or in small organizations. As all the data of Microsoft Outlook is stored in one .PST file on the local computer, you can easily backup or sync your mails. For developers, with the Messaging API and Outlook Object Model, it’s also convenient to access all the data in the .PST file. If you want to get more Portable Executable Information of PST format, you can check this article: outlook.pst.

The .PST format has been increased greatly since the Microsoft Outlook 2003 that provides greater storage capacity (maximum file size 20GB) and Unicode support. And the new version of PST file in Outlook 2003 or Outlook 2007 is not compatible with earlier version of PST file (ANSI encoding). Because the PST file is saved on your computer and there’s limitation of the mailbox size, then, you may need to compact them to reduce the size.

PST files are extremely important for your mails. It’s necessary to apply protection on them. However, password protection of PST files is not so secure technically, since there have been tools that can remove or bypass the password protection.

How about Microsoft to Open up PST Format

Better late than never, Microsoft Outlook will become open source partly. The documentation on Outlook Personal Folders (.PST) is still in beginning period, but it will give detailed information on structure, data storage and accessing of PST file. For example, you could know how to navigate the folder hierarchy, how to access the individual data objects and properties, etc.

As the documentation will be in the Open Specification Promise, then anyone could take advantage of the .PST file format freely. And as the result, interoperability of Microsoft Outlook with other applications will be more facilitative. Microsoft will also benefit from the open up of .PST format. It may be helpful to make .PST format as one standard in E-mail data storage area. In the end, if you are interested in the document drafts of the .PST file format, just send message to pstinfo@microsoft.com.