How to Fix PST Is Not an Outlook Data File
In short: The “PST is not an Outlook Data File” error means Outlook cannot read the .pst you are opening, usually because it is corrupt, marked read-only, moved to a network drive or oversized. The quick fixes are to clear the read-only flag and run ScanPST.exe from the correct Click to Run folder. If the file is badly damaged, a repair tool rebuilds it into a clean PST.
What the error means and why it happens
A PST (Personal Storage Table) is the file Outlook for Windows uses to keep your emails, contacts, calendar and tasks on your computer. The format belongs to Outlook, which is strict about the exact structure, so one small problem inside the file stops the whole thing from mounting. The error almost always traces to one of these:
- Corruption, from Outlook closing during a write, a power cut, a virus or bad sectors on the disk.
- A read-only or hidden attribute, so Outlook can see the file but refuses to mount it as a working data file.
- A network or USB location, which Outlook does not support for a live .pst.
- An oversized file, which passes its size limit and turns unstable.
- A wrong or missing extension, where the file is not really a .pst or was built by a non-Outlook program.
Knowing your cause tells you which fix to start with. A read-only flag clears in seconds, while real corruption needs ScanPST or a repair tool.
Backup and Recovery Specialist, Corbett Software
“I have hit this on plenty of machines while moving old archives around. It always looks scarier than it is. Clear the read-only flag, copy the file to a local folder and run ScanPST. Most cases are done there. Only a badly broken file needs a proper repair tool. Even then the data usually comes back.”
Quick checks first
Three of these take under a minute, so try them before anything heavier.
- Check the extension is .pst. Right-click the file, choose Rename and confirm it ends in .pst, not .pst.txt or a wrong extension. A file that is not really a PST throws this exact error.
- Clear the read-only and hidden flags. Close Outlook, right-click the .pst, choose Properties, then on the General tab uncheck Read-only and Hidden and click Apply. This alone fixes files that came off a CD, a backup drive or a locked folder.
- Copy it to a local folder. Outlook does not support a live .pst on a network share or a USB drive. Copy it to Documents, then open it through File, Open and Export, Open Outlook Data File.
- Make sure it is not in use. If another window or a background process has the file open, close Outlook fully and try again.
Repair the PST with ScanPST
ScanPST.exe, the free Inbox Repair Tool, ships with Outlook and fixes minor structural errors. The trick is finding it, since most old guides point to the wrong folder. On a current Click to Run install it lives here:
| Install type | ScanPST.exe location |
|---|---|
| Microsoft 365, 2024, 2021, 2019 (Click to Run) | C:Program FilesMicrosoft Office ootOffice16 |
| Older 32-bit MSI install | C:Program Files (x86)Microsoft Office ootOffice16 |
| Outlook 2013 / 2010 / 2007 | Office15 / Office14 / Office12 in the same path |
- Close Outlook, open that folder and run ScanPST.exe.
- Click Browse, select the problem .pst, then Start.
- If it reports errors, click Repair. It makes a backup copy of the file first.
One note: the new Outlook for Windows, the rebuilt app, does not use PST files and has no ScanPST, so this fix applies to classic Outlook only.
Fix an oversized PST
A PST that passes its size limit becomes unstable and can trigger this error. The limit depends on the Outlook version:
| Outlook version | PST type | Size limit |
|---|---|---|
| 97 to 2002 | ANSI | 2 GB |
| 2003, 2007 | Unicode | 20 GB |
| 2010 to 365 | Unicode | 50 GB |
If your file is near or over its limit, trim it. Export older folders to a separate .pst or archive them, so the working file drops back under the ceiling. Our guide on how to reduce your Outlook mailbox size walks through this.
If it still will not open
When the quick fixes and ScanPST do not clear it, work through these.
- Check the disk. A failing drive keeps re-corrupting the file. Open Command Prompt as administrator and run chkdsk C: /f /r on the drive that holds the .pst, then repair it again.
- Disable add-ins. A faulty add-in can block the file. Start Outlook in Safe Mode with outlook.exe /safe. If the error is gone, open File, Options, Add-ins, then COM Add-ins and Go, then untick recent or unneeded add-ins.
- Update Outlook. An outdated build can misread a file a newer one handles. Go to File, Office Account, Update Options, then Update Now.
- Create a new profile. Open Control Panel, Mail, Show Profiles, Add, name it, set it as default and attach the .pst. The old profile stays, so nothing is lost.
Recover a badly corrupt PST
When every native fix fails, the file is damaged beyond what ScanPST can rebuild. The safe move then is to read the mailbox with a dedicated repair tool and write it back to a clean file, so you do not lose the data inside.
The Corbett Backup and Restore Wizard reads a broken .pst, previews every item so you can confirm nothing is missing, then exports it to a clean PST, PDF or another format any program can open. It handles files that ScanPST gives up on, keeps the full folder tree, then offers a free demo edition on every edition of Windows.
- Open the tool, click Open and add the damaged .pst.
- Let it scan, then preview the recovered mailbox to confirm the items are intact.
- Choose your output, a fresh PST or PDF, pick a location and run the export.
If you would rather not run the free scan, here is how to repair a PST without the ScanPST tool.
Frequently asked questions
Why does Outlook say my PST is not an Outlook Data File when it opened yesterday?
Something changed the file between sessions, usually a read-only flag, a move to a network drive or corruption from an unclean shutdown. Clear the read-only box first, then run ScanPST.
Where is ScanPST.exe on Microsoft 365 or Outlook 2021?
On a Click to Run install it sits in C:Program FilesMicrosoft Office
ootOffice16, not the old Program Files (x86) path that pre-2019 guides list.
Can ScanPST fix every PST error?
No. It repairs minor structural damage. If the header is badly broken or the file came from a non-Outlook program, ScanPST cannot rebuild it and you need a dedicated repair tool.
What is the PST file size limit?
Older ANSI PSTs cap at 2 GB, Unicode PSTs in Outlook 2007 at 20 GB, then Outlook 2010 and later at 50 GB. Passing the limit can make the file unstable and cause this error.
Does the new Outlook for Windows have an Inbox Repair Tool?
No. The rebuilt new Outlook does not store mail in PST files, so there is no ScanPST. These fixes apply to classic Outlook only.
Will repairing the PST delete any of my emails?
ScanPST tries to keep everything and makes a backup copy first. A good repair tool previews the data before export, so you can confirm nothing is missing.