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Outlook "file .pst is not an Outlook data file": causes and fixes

Short answer

Outlook opened the file but could not read a valid Outlook data file structure in it. Usually the .pst is damaged, only partly copied, or blocked (read-only or an online-only OneDrive file). Copy it to a local folder, clear the Read-only attribute, then run the Inbox Repair Tool (SCANPST.EXE) on it and open it again with File > Open & Export > Open Outlook Data File.

What this message means

A .pst (Personal Storage Table) file stores email, contacts and calendar items on your computer. Before loading one, Outlook checks the file header to confirm it is a real Outlook data file. When that check fails, you get this message. It does not always mean your mail is gone: most often the file is corrupted, only half copied, locked by Windows or OneDrive, or it is actually a different kind of file with a .pst name. If the error names a file ending in .ost instead, it is the cache file for an Exchange, Microsoft 365 or Outlook.com account, and Outlook can rebuild it from the server.

Common causes

CauseHow to tell
The .pst file is corruptedThe file is a normal size (megabytes or gigabytes), but the error started after Outlook crashed, the PC shut down unexpectedly, or a USB drive was pulled out while Outlook was running.
The copy or download was incomplete, or the file is not really a .pstIn File Explorer the file shows 0 KB or is much smaller than expected, or it came from a Mac (an .olm export renamed to .pst), a ZIP that was not fully extracted, or an interrupted transfer.
Windows or OneDrive is blocking access to the fileThe file sits on a CD/DVD, network share or USB stick, has Read-only ticked under Properties > General > Attributes, or shows a cloud icon in File Explorer (OneDrive online-only).
The offline cache (.ost) file is damagedThe error names a file ending in .ost in C:\Users\<name>\AppData\Local\Microsoft\Outlook and appears as "Cannot start Microsoft Outlook. The set of folders cannot be opened." Outlook on the web still works fine.
An old ANSI-format .pst hit its 2 GB limitThe file was created by Outlook 2002 or earlier and its size is right around 2 GB (about 1.99 GB).
The Outlook profile points to a renamed, moved or broken fileOutlook shows the error at every startup for the same path, even though you moved or renamed that file, or other .pst files open fine.

How to fix it

1. Copy the file locally and remove Read-only

Classic Outlook for Windows (Windows 10 and 11)

  1. Close Outlook.
  2. If the file is in OneDrive, right-click it in File Explorer and choose Always keep on this device, then wait until the cloud icon becomes a green check mark.
  3. Copy the .pst to a local folder such as Documents\Outlook Files. Don't open it straight from a USB stick, DVD or network drive.
  4. Right-click the copied file, choose Properties, clear Read-only (and Hidden) under Attributes, then click OK.
  5. Check the size on the General tab. If it is 0 KB, the file holds no data. Go back to the original source or a backup.
  6. Open Outlook and go to File > Open & Export > Open Outlook Data File, then select the copied file.

2. Repair the .pst with the Inbox Repair Tool (SCANPST.EXE)

Classic Outlook for Windows (Microsoft 365, 2016, 2019, 2021, 2024)

  1. Close Outlook completely.
  2. Open File Explorer and go to C:\Program Files\Microsoft Office\root\Office16 (64-bit Office) or C:\Program Files (x86)\Microsoft Office\root\Office16 (32-bit Office). If SCANPST.EXE isn't there, search the Office folder for scanpst.exe.
  3. Run SCANPST.EXE, click Browse and select the .pst file, then click Start.
  4. If errors are found, keep "Make backup of scanned file before repairing" ticked and click Repair.
  5. Run the scan again until it reports no errors, then open the file in Outlook.

3. Rebuild a damaged .ost cache file

Exchange, Microsoft 365, Outlook.com and IMAP accounts only (not POP or archive .pst files)

  1. Close Outlook.
  2. Press Windows key + R, type %localappdata%\Microsoft\Outlook and press Enter.
  3. Find the .ost file named in the error and rename it (for example, add .old to the end).
  4. Start Outlook. It creates a new .ost and downloads your mail from the server again. On large mailboxes this can take a while.

4. Create a new Outlook profile

Classic Outlook for Windows

  1. Close Outlook.
  2. Open Control Panel, search for Mail, and open Mail (Microsoft Outlook).
  3. Click Show Profiles, then Add, enter a name, and set up your email account.
  4. Select "Always use this profile", choose the new profile, and click OK.
  5. Start Outlook, then attach the repaired .pst with File > Open & Export > Open Outlook Data File.

5. Repair the Office installation

Windows 11: Settings > Apps > Installed apps. Windows 10: Settings > Apps > Apps & features

  1. Close all Office apps.
  2. Open the Apps list in Settings and find Microsoft 365 or Microsoft Office.
  3. Windows 11: click the three dots, then Modify. Windows 10: select the app, then Modify.
  4. Choose Online Repair and click Repair. It needs an internet connection and can take 10 to 30 minutes.
  5. Restart the PC and open the .pst again.

6. Recover the file from a backup or an older copy

  1. If SCANPST cannot repair the file, or reports it can't recognize it, it may be too damaged or not a .pst at all.
  2. Right-click the folder that held the file, choose Properties > Previous Versions (if File History or restore points are on) and restore an earlier copy.
  3. Check OneDrive version history (right-click the file > Version history) or any external backup.
  4. Ask whoever sent the file to export it again from classic Outlook with File > Open & Export > Import/Export > Export to a file > Outlook Data File (.pst).

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Still not fixed?

If SCANPST reports the file can't be recognized even after a fresh copy, the file is probably not a .pst or is too damaged for Microsoft's tools. Try an older backup first. For work accounts, contact your IT department: your mail is stored on the Exchange or Microsoft 365 server, and they can restore deleted items or export a new .pst from the server. For personal archives with no backup, a third-party PST recovery tool is the last option. Test its free preview before paying, and always work on a copy of the file.

Questions people ask

Will SCANPST delete my emails?

It can remove items it can't repair, which is why you should keep "Make backup of scanned file before repairing" ticked. Items it recovers without a folder go into a Recovered Personal Folders or Lost and Found folder.

Where is SCANPST.EXE in Microsoft 365?

It's usually in C:\Program Files\Microsoft Office\root\Office16 for 64-bit Office, or C:\Program Files (x86)\Microsoft Office\root\Office16 for 32-bit Office. It doesn't appear in the Start menu, so open it from File Explorer.

Can I open a .pst file in the new Outlook for Windows?

Yes, through Settings > Files > Outlook Data Files > Add file. Classic Outlook must also be installed with the same 32-bit or 64-bit architecture, you need a Microsoft 365 subscription, and it doesn't work on ARM devices.

Can Outlook for Mac open a .pst file?

Not directly. In legacy Outlook for Mac, go to Tools > Import, choose Outlook for Windows archive file (.pst), and click Continue. The imported items appear under On My Computer.

Is it safe to delete the .ost file?

Yes, for Exchange, Microsoft 365, Outlook.com and IMAP accounts, because the mail is stored on the server and Outlook downloads it again. Never delete a .pst this way. It is often the only copy of that mail.

Sources

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