What Is A Personal Storage Table (PST) File? - Fortinet

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Definition, security issues, and frequently asked questions about PST files.

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PST File Meaning

A PST file is a personal storage table, which is a file format Microsoft programs use to store items like calendar events, contacts, and email messages. PST files are stored within popular Microsoft software like Microsoft Exchange Client, Windows Messaging, and Microsoft Outlook.

The PST file format is also commonly referred to as a personal folder, or when used as a cache in Outlook’s exchange mode, an offline storage table (OST) or offline folder. The format first appeared in the mid-1990s in the Microsoft Exchange email client, which later became Microsoft Outlook. It was used to help users access server mailboxes, and just like in the modern day, allow them to create local archives of the email folders they have on server-based email clients.

When a new email account is added to Outlook, Outlook creates a local copy of the information onto the user’s device. This enables users to access emails they have previously downloaded or synchronized, contacts and calendar information, and tasks even if they are not online. Some Microsoft accounts, such as Post Office Protocol (POP) accounts, store information in Outlook Data Files (.pst), while others, such as Outlook 365, Exchange, Internet Message Access Protocol (IMAP), and Outlook.com accounts, store information in Offline Outlook Data Files (.ost).

Archiving emails is now associated with terms and practices like electronic discovery (e-discovery), compliance, and regulation. But PST files were originally used to help admins limit the amount of storage available on their servers to improve performance and reduce backup times. This also enabled users to expand their email storage space by creating local archives.

Every email account created in Outlook gets its own database, which is the PST file that stores contacts, calendar items, emails, and reminder messages. This data can either be compressed or encrypted, and Outlook’s performance slows down as the PST file accumulates more data. 

PST files appear with a .pst extension in an Outlook data folder, while .ost files are used as a temporary offline storage option for Exchange servers and webmail hosts, such as Outlook.com. This helps users access emails even when they are not connected to the email server.

What Are The Advantages of PST files?

The main business advantage of using PST files is to reduce the amount of data residing on email servers. This reduces the amount of time that admins have to spend helping end-users who have reached the maximum capacity of their inbox. 

End-users benefit from gaining extra space to store their emails. They are also able to access the data stored in their email inbox when they are offline.

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PSTs And Security Issues

PST files are an extremely common form of email storage, which are central to all Microsoft email software solutions. However, if they are managed incorrectly, they can become corrupted or create a major security issue.

Its widespread use makes email one of the most common threat vectors targeted by cyber criminals. The sophistication and volume of email-based attacks continues to increase, especially as people move to cloud-based email solutions such as Microsoft 365, Outlook.com, and Google’s Gmail and G Suite applications.

As with any Microsoft IT environment, organizations and users must understand the importance of managing PST files securely. This process is crucial to helping businesses prevent data loss and leakage, avoid any legal issues, and protect themselves from cyberattacks that target archived email data.

Part of the problem with PST files is that they were designed for use in a different era of computing, which has seen issues with stability and unexpected access errors. Having local access to email data may sound like a positive concept, but this can easily result in PST files becoming corrupted and users losing access to their email inboxes. Furthermore, the fact that PST files reside on users’ local devices runs the risk of them not being backed up. If that data is lost because of a hard drive crashing or some other computer or device issue, then it is likely unrecoverable. 

However, the tactics deployed to deal with PST files have gradually evolved in line with the sophistication of the devices they are stored on. Tools like PST file repair, migration, storage, and recovery ensure there are now simple solutions for issues that would have been more difficult to remedy. For example, Microsoft’s Inbox Repair tool is specifically designed to help users validate, repair, and correct problems with PST files, enabling them to recover and repair any lost files or personal folders.

PST File FAQs

What is the purpose of a PST file?

A PST file is used by Microsoft programs to store data and items such as email messages, calendar events, and contacts.

Can you open a PST file without Outlook?

Yes. Aside from Outlook, PST files are associated with several Microsoft software services, including Microsoft Exchange Client and Windows Messaging.

How do you create a PST file?

PST files are automatically created by Outlook. However, they can be created manually. From an Outlook inbox, select New Items, then More Items, and Outlook Data File. Create a file name and check the Add Optional Password box, then type in a password and verify it.

Where is a PST file located?

The location of a PST file depends on the version of Outlook that a user is running. Outlook 2007 and Outlook 2010 both store PST files in a user’s AppData folder. That is easily discoverable using the C:\users\username\AppData\Local\Microsoft\Outlook location. Microsoft moved the PST file location into the Documents folder in Outlook 2013 and retained it for Outlook 2016. It can be discovered using this location: C:\users\username\Documents\Outlook Files. 

The PST file location is easily discoverable within all versions of Outlook. In Outlook 2007, open Account Settings from the Tools menu. While in Outlook 2010, Outlook 2013, and Outlook 2016, users can reach the same location by opening the File menu, then the Account Settings dropdown menu, and clicking on Account Settings. From the Account Settings in all Outlook versions, open the Data Files tab, select the account to be investigated, then click on Open File Location. Outlook will then open a File Explorer window that contains the user’s PST and OST files.

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