Tech Corner


Outlook 2003 and PST files

Microsoft Outlook 2003 is now the Agency-standard application for electronic mail. Part of the Microsoft Office suite, Outlook 2003 represents quite a makeover from previous versions as we have noted in past Bulletin articles.

The PST file

One subtle change in Outlook and one that many users may still be unaware of concerns the all important PST file. As used in Microsoft Outlook the acronym “pst” refers to Personal folder Storage. In reference to structures within the Outlook application a PST file is referred to as a Personal Folder File.

If you use Outlook without the benefit of a Microsoft Exchange server then all of your Outlook data is stored in a Personal Folder File. In FEMA we have Exchange servers to host our mail box and we use Personal Folders to archive messages. Many of us have seen the messages from the “System Attendant” advising us that one or more files have been automatically deleted from one of our mail folders. This is a necessary maintenance tool for Exchange administration as without such pruning of messages our mail server would soon be overwhelmed.

Exchange limits the size of your mailbox which includes your inbox, sent items, deleted items, and contacts. Size is not the only limitation as messages are deleted from these folders when they have reached a defined expiration date (usually 90 days). To avoid losing messages from your inbox you should create a Personal Folder. The Personal Folder File, which will have a PST extension, is stored on your hard drive and is thus out of control of the Exchange administrator. By default Outlook will want to place the PST file under the user's Profile Path: Documents and Settings\%user%\Local Settings\Application Data\Microsoft\Outlook, although you can modify this path to place the file wherever you wish. NOTE: the Local Settings folder is hidden by default. To view this folder you must change the View settings under Folder Options in the Tools menu of Windows Explorer.

In all versions of Microsoft Outlook through Outlook 2002 these PST files were stored in the ANSI (American National Standards Institute) format. This format is more specifically known as “Windows ANSI”. It incorporates all English as well as European symbols with one byte, eight bits, to represent each character. These PST files were limited to 2GB in size although the actual functional limit is smaller, around 1.82GB. A PST file that grows larger than this is subject to corruption. The actual file may cease to function and data could be irrevocably lost. Worse yet there is no mechanism within Outlook to warn you that your PST file has grown too large and is subject to a major malfunction.

Outlook 2003 now supports PST files using the UNICODE format. UNICODE is an International 16-bit character set designed to represent all the characters of all the world's languages. These UNICODE-formatted PST files can grow to 33TB (terra bytes) in size. This is an awesome increase in capacity however some experts advise limiting even the UNICODE-based PST file to a maximum of 5GB.

With Outlook 2003 there is still support for PST files created under the ANSI format. When you first set up a Personal Folder or integrate an existing PST file into a fresh installation of Outlook 2003 you will be prompted to choose which format to use: “Office Outlook Personal Folders File (.pst)” (selected) indicates the new UNICODE format. The other option, “Outlook 97-2002” provides support for PST files created under earlier editions of Outlook using the ANSI standard.

A major point as shown in the dialogue box above is that UNICODE format PST files cannot be opened in earlier versions of Outlook.

If you have saved a PST file created from an earlier version of Outlook, i.e., an ANSI-formatted Personal Folder File and attempt to integrate it into Outlook 2003 as a UNICODE-formatted file the PST file will remain in the ANSI format. To save these messages into the UNICODE format you would have to create a new, UNICODE-formatted Personal Folder and then move all the messages from the ANSI-formatted archive into the new UNICODE archive. There should be no data loss as UNICODE is backward-compatible with ANSI. Conversely if you attempt to move messages from a UNICODE-formatted Personal Folder into an ANSI-formatted Personal Folder there could be data loss if the messages contain any UN ICODE-specific characters. You can have both ANSI and UNICODE Personal Folders in your Outlook 2003 profile. To check the status of your Personal Folder simply right-click the top-level folder, choose Properties and then click the

Advanced tab. Maintenance for PST files

There are some simple maintenance steps you can employ to keep your PST files in good working order. Periodically review your Personal Folder and delete messages that you no longer need. Each Personal Folder will also contain its own Deleted Items folder. Clear the contents of the Deleted Items folder regularly and then compact the Personal Folder to remove empty space. When messages are deleted from a Personal Folder the space those messages occupied in the pst file are not automatically reclaimed. While Outlook does automatically compact PST files during idle time it is just good practice to perform the compacting soon after deleting multiple messages. The “Compact Now” button is under Advanced Settings and can be seen in the above screenshots.

Backing up PST files

A benefit of a Personal Folder file is that it is stored locally on your hard drive and is not subject oversight by the Exchange administrators. The downside is that you must take steps to secure this file. If your hard drive crashes and you have not backed up the file to removable media or a network share then all of your archiving was for naught.

One does not need to be too technically savvy to burn a copy of a PST file to a CD; however given the large size of some PST files a DVD may be necessary to copy the entire file. If you don't have a CD or DVD burner then backing the PST file up to a network share may be your only option.

Microsoft offers a utility to automate the process of backing up PST files. The Personal Folders Backup add-in can be used with Outlook 2000, 2002, and 2003. This tool is available at:

Repairing PST Files

Another handy utility to use is the inbox repair tool which is installed by default during the Outlook installation. This tool, scanpst.exe, can be used to scan PST files for errors. It is located under

\Pro gram FiIes\Common FiIes\System\MSMAPI\1033 and can only be run with Outlook closed. You will be prompted to enter the PST file you wish to scan or you can browse for the file. The tool executes 8 stages in scanning the PST file for errors.

Ideally the scan will not find errors: The 2GB Truncation Tool

An ANSI-formatted PST file that has grown beyond the 2GB limitation and is corrupted may produce an error when you open Outlook. The official fix for such a problem, according to Microsoft, is to download the 2GB truncation tool (Oversized PST and OST Crop Tool) from Microsoft Product Support Services (P55), run the tool against the damaged PST file, and then run the inbox repair tool against the new, truncated file. This process and the link to download the Oversized PST Crop Tool can be found at:;en-us;Q296088

Unfortunately some data (messages) may be lost but there is at least some hope of regaining the bulk of your critical mail archives.

Outlook users who employ PST files for archiving mail messages would be well advised to recognize the necessity of performing periodic maintenance and backups to safeguard these valuable archives.





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