How to Open an Outlook Data File (.pst and .ost)
Outlook stores your emails, contacts, calendar entries, and tasks locally in data files — and knowing how to open them can save you from losing important information after a migration, backup, or software reinstall. The process is straightforward once you understand what type of file you're working with and which version of Outlook you're using.
What Is an Outlook Data File?
Microsoft Outlook uses two primary file formats to store data locally:
- PST (Personal Storage Table): The standard data file for POP3, IMAP, and personal archive folders. PSTs are portable — you can move them between computers and import them into a new Outlook profile.
- OST (Offline Storage Table): A local cache of your Exchange, Microsoft 365, or Outlook.com account. OSTs sync with the server and are tied to a specific profile — they aren't directly portable the way PSTs are.
When most people ask how to open an Outlook data file, they're usually working with a .pst file — either a backup, an export from another machine, or an archive.
How to Open a PST File in Outlook 📂
Step 1: Locate the File
Before opening anything in Outlook, know where your .pst file is saved. Common locations on Windows include:
C:Users[YourName]DocumentsOutlook FilesC:Users[YourName]AppDataLocalMicrosoftOutlook
If you received the file from another machine or a backup drive, note its full path.
Step 2: Open the File Through Outlook
- Open Outlook and go to the File tab.
- Select Open & Export (or just Open in older versions).
- Click Open Outlook Data File.
- Browse to the .pst file location and click Open.
The file will appear as a new folder group in your left-hand navigation pane — typically labeled with the name of the original mailbox or "Personal Folders."
You can now browse all the emails, contacts, and calendar items inside it just like any other folder in Outlook.
Step 3: Access the Data
Expand the folder tree in the left pane to explore the contents. If you want to move items into your main mailbox, simply drag and drop them between folders, or use Move to Folder from the right-click menu.
How to Open a PST File Without Outlook
If you don't have Outlook installed, your options are more limited but not zero:
| Method | What It Does | Limitations |
|---|---|---|
| Outlook Viewer (third-party tools) | Read-only access to PST contents | Varies by tool; some charge for export |
| Import into Thunderbird | Free email client can read PSTs via add-ons | Setup required; formatting may vary |
| Online PST converters | Upload and convert to readable formats | Privacy concerns with sensitive email data |
| Install Outlook trial | Full access via Microsoft 365 trial | Requires Microsoft account |
The right method here depends heavily on why you need access — a one-time data recovery situation is very different from a long-term workflow need.
Opening an OST File: A Different Problem
OST files are trickier. Because they're designed as a server-linked cache, Outlook doesn't let you simply import an OST the way you can a PST. If your account is still active and accessible, Outlook will recreate the OST automatically when you log back in — there's often no need to open the old file directly.
If your Exchange account is no longer active, accessing an orphaned OST requires third-party conversion tools that export the contents to PST format first. The quality and cost of these tools varies significantly, and not all of them handle attachments or calendar data reliably.
Factors That Affect How This Works for You 🔧
The process above is consistent across most modern versions of Outlook, but several variables influence the experience:
- Outlook version: Outlook 2010, 2013, 2016, 2019, and Microsoft 365 all support this workflow, but the menu layout differs slightly between versions.
- File size: Very large PST files (especially those over 20–50GB) can be slow to open or may cause performance issues in older Outlook versions.
- File corruption: If a PST was created during an improper shutdown or disk failure, it may not open cleanly. Outlook includes a built-in repair tool called SCANPST.EXE (the Inbox Repair Tool) that can fix minor corruption before you attempt to open the file.
- Encryption or password protection: Some PST files are password-protected. You'll need the original password — there's no built-in recovery option.
- Operating system: This process applies to Outlook on Windows. Outlook for Mac uses a completely different data format (.olm), and the steps for importing or accessing archived data differ entirely.
When the File Won't Open
If Outlook throws an error or the file doesn't appear properly after following the steps above, the most common causes are:
- File path issues — spaces or special characters in folder names can occasionally cause problems
- File corruption — run SCANPST.EXE before trying again
- Version mismatch — PST files created in very old versions of Outlook (pre-2003) use a different format that newer Outlook may not read without conversion
- The file is an OST, not a PST — check the file extension; the two files behave very differently
What works smoothly for someone with a clean backup PST from a recent machine will look quite different from someone trying to recover data from a corrupted or decade-old archive file. The technical steps are the same starting point, but where you land depends entirely on what you're actually working with.