An Overview of Microsoft Outlook PST Files and Reasons for File Corruption

Most people using Microsoft Outlook desktop client know that the application uses PST files for storing data of messages, calendar events, notes, contacts, and everything else it handles. While Outlook is extremely popular all over the world and ranks as the number one desktop email client, the PST file format is not very stable causing Outlook to freeze or deny users access to data due to file corruption. This lack of reliability causes disruption of work, sometimes the loss of valuable data, and considerable time taken to resolve issues that represents an extra burden on IT administrators. While Microsoft does provide a repair tool within Outlook, it is limited in its scope. It is the reason for the IT department to use various third-party PST repair tools for better outcomes.

PST Files – Purpose and Structure

The Microsoft Outlook desktop client automatically creates PST files to store local copies of all email messages received and sent along with their attachments, contacts, task lists, calendar events, and more. Since some PST files have many items in addition to the emails and their attachments that can be quite large, it is not unusual for PST files to be of several GB. While the older versions have a limit of 20 GB, the later versions allow PST files of a maximum of 50 GB.

Outlook 2003 and Outlook 2007 onwards have an “Auto Archive’ function, which is programmed to automatically remove older email messages and data and archive them in a PST file on the local machine. PST files are also commonly used when emails have to be shifted from one system to another, like when you migrate from one mail server to another or when an organization needs to retain a copy of the email of an employee leaving it. PST files represent a convenient method for users to organize and store email data not immediately needed. According to How-To Geek, Outlook users can open PST files without importing them.

The Problem with PST Files

Despite the utility and convenience of PST files, users need to appreciate that it is not a particularly stable file format, especially for storing large amounts of data for the long term. When the PST file size becomes very large, it becomes susceptible to corruption, especially when accessed over a network. PST file issues can occur frequently, and IT administrators can spend a lot of time resolving data corruption issues.

With the growing number of complaints by users, Microsoft recognized the problem of corrupted outlook and introduced enhancements in Exchange 2010 that eliminated the need for users to store email archives locally. However, users who want to can continue to work with PST files even in the current versions of Outlook. While IT administrators can disable the function to prevent users from accessing PST files, many organizations have been using Outlook for a long time and built up a large number of PST files in their archives that they need to access from time to time.

Probable Causes of PST File Corruption 

Because PST files can quickly grow very large, they are especially susceptible to corruption. As users have discovered over many years, there are many reasons for PST files corruption leading to loss of valuable data. Some of the more common ones include:

Hardware failure: PST files, especially large files, tend to lose their integrity when storage devices fail, networks have connectivity problems, and systems crash due to unstable power or power outages. When hardware fails, the storage devices develop bad sectors, and if they happen to be the ones in which PST files are you could potentially lose data. Also, problems in network devices, connectivity, or even power failure can damage PST files.

Software issues: Over the years, users have noticed data corruption due to various issues. For example, Outlook may freeze or throw up error messages in case of a virus attack, incorrect procedures for data recovery, not shutting down Outlook properly, and weaknesses in Outlook programming. The use of inappropriate data recovery tools is one of the top reasons for file damage after relatively minor data corruption, which is why you must know what tools to use and how to use them.

Design problem: Many of the corruption issues of PST files are due to design deficiencies of the earlier versions of Outlook. Users tend to encounter data corruption when the file size is close to or over 2 GB. However, with Outlook 2003 onwards, users can store and access PST files of up to 20 GB and the current versions allow file sizes of 50 GB.


Despite the identified file corruption issues of Microsoft Outlook, it remains one of the most popular email clients in use. Users can prevent PST file corruption to a large extent by implementing various methods like good-quality antivirus programs, installing a UPS for stable power supply, shutting down the computer and Outlook in the prescribed manner, and avoiding accessing PST files over a network. However, some file corruption events are inevitable and require the use of tools for outlook repair

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