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

PST stands for "Personal Storage Table." When you use Microsoft Outlook on your computer, it needs somewhere to keep all your messages, meeting invitations, task lists, and contact information. A PST file is that storage container — it's a single file, usually named something like "Outlook.pst," that sits on your hard drive and holds everything Outlook needs to work.

Think of it like a filing cabinet. Instead of papers scattered across your desk, they're all organized in one place. Outlook reads from and writes to this PST file every time you check email, add a contact, or update your calendar. If you delete the PST file, you lose all that data. If you back it up, you're backing up your entire Outlook life.

PST files are specific to Outlook on Windows and Mac. If you use Outlook on the web (the version you access through a browser), your data lives on Microsoft's servers instead, and no PST file exists on your computer.

Key Takeaways

  • A PST file is a single container on your computer that holds all your Outlook email, calendar events, contacts, and tasks.
  • PST files are created automatically by Outlook on Windows and Mac, but not by Outlook on the web.
  • If you switch computers or want to move your Outlook data, you can export it as a PST file and import it elsewhere.
  • PST files can grow very large over time, which can slow down Outlook or make backing up your computer harder.

Where your PST file actually lives on your computer

On Windows, Outlook typically stores your PST file in a hidden folder. The exact location depends on your Windows version, but it's usually something like C:\Users\[Your Username]\AppData\Local\Microsoft\Outlook. The folder is hidden by default, so you won't see it unless you turn on the option to show hidden files.

On a Mac, the PST file is usually in ~/Documents/Microsoft User Data/Office 2016 Outlook Data or a similar path depending on your Outlook version. Again, you may need to adjust your Mac's view settings to see it.

You don't need to find or move this file yourself under normal circumstances. Outlook manages it automatically. But if you're backing up your computer or moving to a new machine, knowing where it lives helps you understand what's being copied.

When you might export or import a PST file

You create a new PST file manually when you want to move your Outlook data somewhere else. Common reasons include switching to a new computer, sharing your email history with someone else, or archiving old messages to free up space.

To export your Outlook data as a PST file, you go to File > Open & Export > Import/Export in Outlook, then choose "Export to a file" and select PST format. Outlook then creates a new PST file in whatever location you choose — usually your Desktop or Documents folder so you can find it easily.

To import a PST file into Outlook, you use the same Import/Export menu but choose "Import from another program or file" instead. You then select the PST file you want to bring in, and Outlook adds all that data back into your account.

Why PST files can become a problem

PST files grow every time you receive an email or add a contact. Over years of use, a single PST file can reach several gigabytes in size. When a PST file gets too large — typically over 2 GB — Outlook can slow down noticeably. Searching becomes slower, opening folders takes longer, and the whole program feels sluggish.

A bloated PST file also makes backing up your entire computer harder. If your PST file is 5 GB and your backup drive is limited, that one file takes up a huge chunk of your backup space. Some people create separate PST files for different years or projects to keep any single file manageable.

Another risk: if your PST file becomes corrupted — damaged by a crash, a power failure, or a virus — you can lose access to all the data inside it. That's why backing up your PST file separately, in addition to backing up your whole computer, is a reasonable precaution if your email is important to you.

PST files versus cloud-based email storage

If you use Outlook with a Microsoft 365 account (formerly called Office 365), your email can live in the cloud instead of in a PST file on your computer. When you set up Outlook to connect to a Microsoft 365 mailbox, the data syncs to Microsoft's servers, and you can access it from any device.

Cloud storage has trade-offs. You don't have to manage a growing PST file on your hard drive, and your data is backed up automatically by Microsoft. But you're dependent on your internet connection to access everything, and your data lives on servers you don't control.

Some people use both: they keep their active email in a cloud mailbox through Outlook, and they export old PST files as an archive for long-term storage on an external drive. This gives them the speed and accessibility of cloud email without the risk of losing years of old messages.

How to check the size of your PST file

On Windows, open File Explorer, navigate to the folder where your PST file lives (usually the hidden AppData folder mentioned earlier), right-click the PST file, and select Properties. The file size appears in the window that opens.

On a Mac, open Finder, navigate to the folder containing your PST file, right-click it, and select "Get Info." The size is listed in the window that appears.

If your PST file is larger than 2 GB, Outlook may already be running slowly. You can create a new PST file and move older messages into it, or you can archive messages to reduce the size of your main file. Outlook has a built-in archive feature that automatically moves old messages to a separate PST file based on rules you set.

Frequently Asked Questions

Can I open a PST file without Outlook?

Not easily. PST files are proprietary to Outlook, so you need Outlook installed to read them. Some third-party tools claim to open PST files, but they're not made by Microsoft and may not work reliably. Your safest option is to use Outlook itself or to export the PST file to a more universal format like CSV before you uninstall Outlook.

What happens if I delete my PST file?

You lose all the data in it — email, calendar, contacts, everything. If you're using Outlook with a cloud account like Microsoft 365, the data is still on the server, so you can recover it. But if you're using a local PST file only, deletion is permanent unless you have a backup.

Can I have multiple PST files in Outlook?

Yes. You can create separate PST files for different purposes — one for work email, one for personal email, one for archived messages — and open them all in Outlook at the same time. This can help keep your data organized and prevent any single file from growing too large.

Is my PST file automatically backed up?

Only if your computer is backed up. If you use Windows Backup or Mac Time Machine, your PST file is included in those backups. But if you don't back up your computer, your PST file isn't backed up either. Creating a separate copy of your PST file on an external drive is a good extra precaution.