A PST file stores your email, calendar events, and contacts in one place on your computer

PST stands for Personal Storage Table. It is a single file that holds copies of your email messages, calendar appointments, task lists, and contact information. When you use Microsoft Outlook, the program saves everything you receive and create into a PST file on your hard drive. Think of it as a container — the file itself is not the email program, but rather the filing cabinet where Outlook keeps what you have done.

PST files exist because email programs need somewhere to store data locally. When you read messages from a mail server, Outlook copies them into the PST file so you can read them later without being connected to the internet. The same goes for events you create in your calendar or notes you write — they all go into that single PST file until you delete them or archive them somewhere else.

Key Takeaways

  • A PST file is a storage container that holds email messages, calendar events, contacts, and tasks created or received in Microsoft Outlook.
  • PST files live on your computer's hard drive, not on a mail server, so they contain only the data you have downloaded or created locally.
  • Each Outlook account typically has its own PST file, and the file grows larger as you receive more messages and create more calendar entries.
  • You can back up a PST file by copying it to an external drive or cloud storage, which protects your email history if your computer fails.
  • PST files have a size limit — older versions max out around 2 GB, while newer versions can hold up to 50 GB before Outlook may slow down.

Where PST files live on your computer

PST files are stored in a specific folder on your hard drive. On Windows, Outlook usually saves them in a hidden folder at C:\Users\[Your Username]\AppData\Local\Microsoft\Outlook. On a Mac, they go in ~/Library/Group Containers/UBF8T346G9.Office/Outlook/Outlook 15 Profiles/Main Profile/Data. The exact path depends on your version of Outlook and your operating system.

Because these folders are hidden by default, most people never see their PST files. Outlook opens them automatically when you launch the program, so you do not have to think about where they are. However, if you want to back up your email or move it to another computer, you need to know where to find the file. You can unhide the folder in Windows by opening File Explorer, clicking View, and checking the box for "Hidden items."

How large PST files get and when they cause problems

A PST file grows every time you receive an email or create a calendar event. If you have been using the same Outlook account for years and never delete anything, your PST file can become very large. Older versions of Outlook (2002 and earlier) have a hard limit of 2 GB — once the file reaches that size, Outlook stops working properly and may refuse to save new messages. Outlook 2003 and later versions can handle files up to 20 GB or 50 GB depending on the version, but performance often slows down before you hit the limit.

A bloated PST file can make Outlook slow to open, slow to search, and slow to sync with your mail server. If you notice Outlook taking a long time to load or freezing when you try to read messages, a very large PST file may be the reason. You can check the file size by finding the PST file on your hard drive, right-clicking it, and selecting Properties. If it is approaching the limit for your version of Outlook, you should consider archiving old messages or deleting items you no longer need.

Backing up and moving PST files

Because a PST file contains years of email history and calendar data, losing it means losing all that information. The safest approach is to copy your PST file to an external hard drive or cloud storage service like OneDrive or Google Drive. You can do this while Outlook is closed — straightforward navigate to the folder where your PST file lives, copy the file, and paste it onto the backup location.

If you want to move your email to a different computer, you can copy the PST file to that computer and open it in Outlook there. Outlook will recognize the file and load all your messages and calendar events. However, if you are switching from Outlook to a different email program like Gmail or Apple Mail, you may need to export your PST file to a different format first, since not all programs can read PST files directly.

PST files versus cloud-based email storage

PST files are a local storage method — they sit on your computer and contain only what you have downloaded. This is different from cloud-based email, where messages stay on a server and you access them through a web browser or app. Gmail, Outlook.com, and Yahoo Mail all use cloud storage, so your email exists on their servers rather than on your hard drive.

The advantage of PST files is that you own the data and can back it up however you want. The disadvantage is that you have to manage the file size yourself and you cannot access your email from multiple devices unless you sync the PST file across all of them. Cloud-based email is easier to access from anywhere, but you depend on the service staying available and you have less direct control over where your data lives.

When you might need to work with a PST file directly

Most of the time, you never need to think about your PST file — Outlook handles it in the background. However, there are situations where you need to interact with it directly. If Outlook crashes and corrupts the PST file, you may need to repair it using Outlook's built-in repair tool or a third-party utility. If you want to archive old messages to free up space, you can create a separate PST file and move messages into it. If you are switching computers, you can copy the PST file to migrate all your email at once.

You might also need to work with a PST file if you are recovering data from an old computer or if someone asks you to access their Outlook data after they have left a job. In these cases, you can open a PST file in Outlook by going to File, then Open and Export, then Open Outlook Data File, and selecting the PST file you want to load.

Frequently Asked Questions

Can I open a PST file without Outlook?

Not easily. PST files are designed for Outlook, and most other email programs cannot read them directly. However, some third-party tools can convert PST files to other formats like EML or MBOX, which Gmail and other services can import. You can also open a PST file in Outlook on the Web if you have a Microsoft account.

What happens if my PST file gets deleted?

If you delete a PST file and have not backed it up, the email and calendar data in that file is gone. However, if your email account is synced with a mail server (like an Exchange server or Outlook.com), the messages may still exist on the server and you can re-read them. If the account is local-only, the data is lost unless you have a backup copy.

Can I have more than one PST file?

Yes. Outlook can open multiple PST files at the same time. Many people create separate PST files for different email accounts or to archive old messages. You can add a PST file to Outlook by going to File, then Open and Export, then Open Outlook Data File.

Why is my PST file so large?

PST files grow because they store every message you receive and every item you create. If you have been using the same account for many years, never deleted messages, and receive a lot of email, the file can become very large. Attachments take up the most space, so emails with large files attached add more to the PST size than plain text messages do.

Should I move my PST file to cloud storage?

You can back up a PST file to cloud storage like OneDrive, but you should not run Outlook directly from a cloud folder. This can cause sync problems and file corruption. Instead, keep the PST file on your local hard drive and copy it to cloud storage as a backup, or use Outlook's built-in cloud sync features if your account supports them.