Tuesday, 19 March 2013
3/19/2013 08:06:00 pm 0

An introduction to Outlook data files structure:

Outlook data files structure:
Outlook Email application client uses OST and PST file format for storing the user mailbox data.

When you are using Outlook with Exchange, you can save a local copy of the Exchange database on your local system in OST file format. OST file is an exact replica of the mailbox data stored on Exchange. This file provides the ability to work in off line mode. You can read my previous article to know more about,”Exchange cached mode”.

When Outlook is used without Exchange a PST file is created that stores the user mailbox data on his local system. Let’s have a brief look at the structure of OST/PST files.

OST/PST files structure:
It stores the data in B-tree form i.e. the data is arranged hierarchically in form of nodes (512 bytes) and leafs.                                       
  • Outlook 2002 and earlier versions used ANSI file format (extended ASCII with a code page) encoding and 32-bit pointers .This file structure had the 2 GB file size limits.
  • Outlook 2003 and the later Outlook versions support Unicode format for Unicode (UTF-16 little-endian) and 64-bit pointers which overcome the 2 GB limit that occurred in the earlier versions.
If you want to use the PST files created on newer versions of Outlook in earlier versions then, you need to change them its format from Unicode to ANSI.

To do so, follow the given steps:

1.Open Outlook application (2007/2003).
2.Go to File >Data File Management>Add.
3.Select the option Outlook 97-2002 Personal Folders File (PST).
4.Click OK.
5.Click OK to create a new PST file with default name or you can give any desired name to the new PST file to be created.
6.Click OK.
7.Click Close.
8.Go to the bottom of the navigation pane and Click Folder List. Here you can view the new PST file created by you (in step 5).
9.Drag the .pst file data from existing PST to the newly created PST file. It will automatically copy the data from the existing PST file (Unicode format) to the new PST file (ANSI format).

You can easily perform the above steps if you want to use the Unicode formatted PST files into earlier versions of Outlook.

Note: After conversion of the Unicode formatted PST file data to ANSI format, the Unicode characters used in your PST file (messages or other items) will be lost.

These steps are okay if you want to copy data from a PST file to another PST file. But what to do if you require copying data from an OST file to PST file. There can be various possible scenarios when you need to convert OST file data to PST file format. There is no direct method to migrate between the two Outlook data files manually. For migrating OST file data to a PST file, you would require some tool that can help you to perform an efficient OST to PST conversion.


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