A PST file is Outlook's way of storing your email, calendar, contacts, and tasks on your computer

PST stands for Personal Storage Table. It is a single file that holds copies of messages, calendar events, contact records, and task lists from Microsoft Outlook. When you set up Outlook to work with an email account, the program can store everything locally on your hard drive in a PST file instead of keeping it only on the email server.

The file itself is just a container — think of it like a filing cabinet that Outlook reads and writes to. You can see it in Windows File Explorer as a file with a .pst extension, usually several hundred megabytes to several gigabytes in size depending on how much email you have accumulated.

PST files are specific to Outlook. Other email programs like Gmail, Apple Mail, or Thunderbird use different storage formats. If you switch email clients, you will need to export your PST data into a format the new program can read.

Key Takeaways

  • A PST file contains email messages, calendar events, contacts, and tasks that Outlook stores on your computer rather than only on a mail server.
  • Outlook creates and manages PST files automatically when you add an email account, though you can also create additional PST files manually for archiving or organization.
  • PST files have a practical size limit — Outlook 2010 and earlier versions cap out at 2 GB, while Outlook 2013 and newer support up to 50 GB.
  • You can back up a PST file by copying it to an external drive or cloud storage, which preserves your email and calendar data even if your computer fails.
  • If a PST file becomes corrupted, Outlook includes a repair tool called Scanpst.exe that can often recover the data inside.

When Outlook creates a PST file automatically

Outlook generates a PST file the moment you add an email account to the program. The location and name depend on your version of Outlook and your operating system. On Windows 10 and 11 with recent versions of Outlook, the default PST file is usually stored in a hidden folder at C:\Users\[YourUsername]\AppData\Local\Microsoft\Outlook.

The file is typically named after your email address or account name — for example, yourname@company.com.pst. Outlook opens this file every time you launch the program and closes it when you exit, syncing any changes you made to your email, calendar, or contacts.

If you use Outlook with an Exchange Server account (common in workplaces), the behavior is different. Exchange keeps the master copy on the server, and Outlook downloads a copy to your computer for faster access. This cached copy is stored in an OST file, not a PST file. The distinction matters because OST files are temporary — if you delete them, Outlook will re-download everything from the server. PST files are permanent storage on your machine.

What data lives inside a PST file

A PST file is divided into folders that mirror what you see in Outlook. The main sections are Inbox, Sent Items, Drafts, Deleted Items, and any custom folders you create. Each folder holds email messages with their full text, attachments, sender information, and timestamps.

Beyond email, a PST file also stores your calendar events, including the date, time, description, and any attendees or reminders you set. Contact records are included too — names, email addresses, phone numbers, and notes you have added. If you use Outlook's Tasks feature, those items are stored in the PST as well.

Attachments are embedded directly in the PST file, not stored separately. A 500 MB email with a large video attachment takes up 500 MB of space inside the PST. This is why PST files grow quickly if you receive many messages with files attached.

PST file size limits and when they matter

Older versions of Outlook have a hard ceiling on PST file size. Outlook 2007 and earlier versions max out at 2 GB — once a PST reaches that limit, Outlook stops accepting new messages and you cannot add more data. Outlook 2010 also caps at 2 GB. Outlook 2013 and all newer versions, including Outlook in Microsoft 365, support PST files up to 50 GB.

If you are using an older version of Outlook and your PST approaches 2 GB, you have two options: create a new PST file and move older messages into it (called archiving), or upgrade to a newer version of Outlook. Many people create separate PST files by year or project to keep individual files manageable and to organize their data.

You can check the size of your PST file by right-clicking it in Windows File Explorer and selecting Properties. The file size will show in bytes, kilobytes, or gigabytes depending on how large it is.

How to find and back up your PST file

Locating your PST file depends on your operating system and Outlook version. On Windows, open File Explorer and navigate to C:\Users\[YourUsername]\AppData\Local\Microsoft\Outlook. The AppData folder is hidden by default, so you may need to enable "Show hidden files" in View options first. On a Mac, PST files are typically in Users/[YourUsername]/Documents/Microsoft User Data/Office 2011 Identities or a similar path depending on your Outlook version.

Once you find the file, you can back it up by copying it to an external hard drive, USB stick, or cloud storage service like OneDrive or Google Drive. Close Outlook before copying — if Outlook is running, the file may be locked and the copy could be incomplete or corrupted. After copying, verify that the backup file is the same size as the original.

Regular backups protect you if your computer fails, gets stolen, or your hard drive crashes. A PST file backup is one of the most important things you can preserve because it holds years of email history, calendar records, and contact information that would be difficult or impossible to recover otherwise.

Repairing a damaged PST file

PST files can become corrupted if Outlook closes unexpectedly, your computer loses power during a sync, or the file is damaged by malware. When this happens, Outlook may fail to open, show error messages, or lose access to some of your data.

Microsoft includes a repair tool called Scanpst.exe (Inbox Repair Tool) with Outlook. On Windows, it is usually located at C:\Program Files\Microsoft Office\Office16 (the exact path varies by Office version). On a Mac, the tool is called Rebuild. Running Scanpst.exe scans the PST file for errors and attempts to repair them. The process can take anywhere from a few minutes to several hours depending on file size.

Before running the repair tool, close Outlook completely and make a backup copy of the PST file in case the repair process makes things worse. If Scanpst cannot fix the problem, you may need to restore from a backup or contact Microsoft support.

PST files versus other Outlook storage formats

Outlook uses different file formats depending on the email account type and version. The main alternatives are OST files and IMAP storage. An OST file (Offline Storage Table) is used with Exchange Server accounts and is meant to be temporary — it syncs with the server and can be deleted and re-downloaded. A PST file is permanent storage on your computer and does not sync with a server.

If you use an IMAP email account (common with Gmail, Yahoo, and other web-based providers), Outlook stores messages on the server and downloads copies locally. These copies are not stored in a separate PST file the way they would be with a POP3 account — instead, they are managed within Outlook's database structure.

When you need to move email from one computer to another or switch to a different email program, PST files are the easiest format to work with because they are self-contained and portable. You can copy a PST file to another computer, open it in Outlook there, and all your messages and calendar data come with it.

Frequently Asked Questions

Can I open a PST file without Outlook?

Not directly — PST files are proprietary to Outlook and require the program to read them. However, you can export the contents of a PST file to other formats like CSV (for contacts) or ICS (for calendar events) using Outlook's export feature, then open those files in other programs. Some third-party tools claim to read PST files, but they are not officially supported by Microsoft.

What happens if I delete my PST file?

If you delete a PST file and have not backed it up, the data inside is lost. Outlook will no longer show those messages, calendar events, or contacts. If the PST was your only copy of that data (not synced with a server), recovery is difficult. If you accidentally delete a PST, stop using your computer immediately and contact a data recovery service — they may be able to retrieve the file from your hard drive before it is overwritten.

Can I have multiple PST files in Outlook?

Yes. You can create additional PST files manually and open them in Outlook alongside your main PST. This is useful for archiving old email, organizing by project, or keeping work and personal email separate. In Outlook, go to File > Open & Export > Open Outlook Data File to add an existing PST, or create a new one through the same menu.

How big can a PST file get before Outlook has problems?

Outlook 2013 and newer versions support PST files up to 50 GB without hard limits, but performance can slow down as files approach that size. Many users find that PST files over 10 GB become noticeably slower to search and navigate. If your PST is large, consider splitting it into multiple files or archiving older messages to a separate PST.

Is a PST file the same as an email backup?

A PST file is a backup of your Outlook data, but only if you store it separately from your computer. If your PST file sits only on your hard drive and your computer fails, you lose both the original and the backup. A true backup means copying your PST to an external drive, cloud storage, or another computer so that if your main computer is damaged or stolen, your data still exists elsewhere.