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

PST stands for Personal Storage Table. It is a single file that holds copies of your messages, calendar events, contact lists, and notes — everything you see in Microsoft Outlook. When you open Outlook, it reads from this file to show you your inbox and folders. If you back up your PST file, you back up your entire Outlook history.

The file itself is invisible in normal use. You do not see it sitting on your desktop or in your Documents folder. Instead, Outlook manages it behind the scenes. On Windows computers, Outlook typically stores the PST file in a hidden folder deep in your user directory. On a Mac, it lives in a different location but serves the same purpose.

PST files matter because they are portable. You can copy a PST file from one computer to another and import it into Outlook on the new machine. This is how people move their entire email history when they switch computers or want to back up years of messages.

Key Takeaways

  • A PST file is a single container that holds all your Outlook email, calendar events, contacts, and notes in one place on your computer.
  • Outlook creates and manages the PST file automatically — you do not have to create it yourself or think about it during normal use.
  • You can export your PST file as a backup, which preserves your entire Outlook history in case you need to restore it later.
  • PST files have a size limit (usually around 50 gigabytes), so very old Outlook accounts with decades of mail may need to be split into multiple files.

How Outlook creates and uses your PST file

When you first set up an email account in Outlook, the program creates a PST file automatically. Every time you receive a message, Outlook writes it to this file. Every time you create a calendar event or add a contact, that information goes into the same PST file. You never have to manually save anything — Outlook does this constantly in the background.

The file grows larger over time as you accumulate more messages and calendar entries. A PST file from someone who has used Outlook for ten years might be several gigabytes in size. A brand-new Outlook account might have a PST file that is only a few megabytes.

Outlook keeps only one PST file active at a time for your main account, though you can create additional PST files if you want to organize mail separately. Some people create a second PST file for archived messages they want to keep but do not access often.

Why you might need to find or back up your PST file

Most of the time you never need to think about your PST file. But there are situations where you need to locate it or make a copy. If your computer crashes and you want to preserve your Outlook data before reinstalling Windows, backing up the PST file is the fastest way. If you are switching to a new computer and want to bring all your old messages with you, exporting the PST file lets you do that.

You might also need to find your PST file if Outlook is running slowly or if you want to move it to a different hard drive to free up space on your main drive. In these cases, knowing where the file lives and how to work with it becomes useful.

Backing up a PST file is straightforward: you locate the file on your computer, copy it to an external drive or cloud storage, and keep it somewhere safe. If something goes wrong with Outlook later, you can restore from that backup.

The difference between PST files and cloud-based email

PST files are local — they live on your computer's hard drive. This is different from cloud-based email like Gmail or Outlook.com, where your messages live on a company's servers and you access them through a web browser or an app that downloads them temporarily.

If you use Outlook with a Gmail account or an Outlook.com account, Outlook still creates a PST file on your computer, but it also keeps a copy on the company's servers. This means your mail is backed up in two places. If your computer dies, your messages are still safe on the server. If the server has a problem, your local PST file still has your messages.

With older email accounts or corporate email systems, the PST file might be the only copy you have. This is why backing up a PST file is more critical for those accounts than for cloud-based email.

PST file size limits and what happens when they fill up

PST files cannot grow infinitely. Outlook has a maximum size limit, usually around 50 gigabytes for modern versions. If you have been using Outlook for many years and have never deleted anything, you might approach this limit.

When a PST file gets very large, Outlook can slow down noticeably. Searching through messages takes longer. Opening folders takes longer. The program might freeze temporarily while it reads through the massive file.

If you hit the size limit, Outlook stops accepting new mail until you reduce the file size. The solution is to create a second PST file and move older messages into it, or to delete messages you no longer need. Many people archive old messages into a separate PST file and keep only recent messages in their active file.

How to locate your PST file on Windows and Mac

On Windows, your PST file is usually hidden inside a folder that Windows does not show by default. The path is typically something like C:\Users\[Your Username]\AppData\Local\Microsoft\Outlook. To find it, you need to turn on the option to show hidden files in Windows File Explorer, then navigate to that folder.

On a Mac, the PST file location depends on your Outlook version. For recent versions, it is usually in Users/[Your Username]/Documents/Microsoft User Data/Office 2019 Identities/Main Identity/Data Records. Again, you may need to show hidden files to see it.

The easiest way to find your PST file without navigating folders is to use Outlook itself. In Outlook on Windows, go to File, then Account Settings, then Account Settings again, then the Data Files tab. You will see a list of all your PST files and their locations. On a Mac, the process is similar but the menu path is slightly different.

What happens to your PST file when you upgrade or switch email providers

If you upgrade to a newer version of Outlook, your PST file comes with you. The new version reads the old file without any problem. Your messages, calendar, and contacts are all still there.

If you switch from Outlook to a different email program like Thunderbird or Apple Mail, you can export your PST file and import it into the new program. Not every program handles PST files perfectly, but most email clients have a way to read them or convert them.

If you switch email providers — for example, from a corporate email system to Gmail — you can export your PST file and import it into Gmail, though the process is more involved than straightforward opening the file. You may need to use a conversion tool or import the messages one folder at a time.

Frequently Asked Questions

Can I open a PST file without Outlook?

Not directly. A PST file is a proprietary format that Outlook created, so you need Outlook or a compatible program to read it. Some third-party tools can open PST files, but they are not made by Microsoft. The safest way to access a PST file is to use Outlook itself.

Is my PST file the same as my email account?

No. Your PST file is a local copy of your messages. Your email account lives on a mail server somewhere. If you delete a message from your PST file, it does not delete it from the server (unless you are using a cloud-based account like Outlook.com). The PST file is just Outlook's way of storing a copy on your computer.

What happens if my PST file gets corrupted?

If a PST file becomes corrupted, Outlook may not be able to read it. You might see error messages or find that some messages are missing. This is why backing up your PST file regularly is important. If corruption happens, you can restore from your backup. Outlook also has a built-in repair tool called Inbox Repair Tool (scanpst.exe) that can sometimes fix minor corruption.

Can I have multiple PST files in Outlook at the same time?

Yes. You can create additional PST files and open them all in Outlook simultaneously. Many people do this to keep archived messages separate from active messages, or to organize mail by year or project. Each PST file appears as a separate folder in your Outlook sidebar.

How often should I back up my PST file?

That depends on how much new mail you receive and how important it is to you. If you use Outlook with a cloud-based account, the server backs up your messages automatically, so a local backup is less critical. If you use Outlook with a corporate or local email account, backing up your PST file monthly or quarterly is a reasonable approach.