How to Fix PST Is Not an Outlook Data File

You double-click an old archive and Outlook answers "File is not an Outlook data file (.pst)". Years of mail sit behind that message, and it feels gone. In most cases your mail is still inside your file. One flag, one wrong folder or one broken header triggers it, and nine fixes below match eight causes.

Why does Outlook say PST is not an Outlook data file?

Outlook says PST is not an Outlook data file when it cannot read your file as valid PST. PST files hold mail, contacts, calendars and tasks in strict structure. One damaged block or wrong attribute stops Outlook from mounting it. Eight causes cover almost every PST error:

• Corruption from power cuts, forced shutdowns, bad disk sectors or viruses.
• Read-only or hidden flag on files copied from a CD, backup drive or locked folder.
• A network share or USB drive. Outlook does not support live PST files there.
• Wrong extension. Renamed OST files, .pst.txt names and files from other programs are not PST files.
• An empty or truncated file, like 0 KB copies from failed backups.
• A size above its limit, which makes PST files unstable.
• An outdated Outlook build, bad add-in or broken Outlook profile.
• A PST still open in another window or background process.

Real user reports match these causes. One TechSpot user restored a PST backup from a reimaged PC, got that message in Outlook 2010 and 2013, and saw other PST files from that folder import fine. One Slipstick forum user lost access to a 7 GB archive after a ransomware infection, and one reply asked whether a virus changed the file extension. One Microsoft Q&A thread on corrupt PST files lists sudden shutdowns, oversized files, drive errors, virus attacks and network drops.

How to fix PST is not an Outlook data file with quick checks?

Start with five checks that take under two minutes. They fix many PST errors with no repair tool.

1. Turn on file name extensions in File Explorer, then confirm your file ends in .pst, not .pst.txt or .ost.
2. Check file size. A 0 KB or tiny file holds nothing, so restore from a backup.
3. Close Outlook fully. End any OUTLOOK.EXE process in Task Manager.
4. Right-click your PST, select Properties, clear Read-only and Hidden, then select Apply.
5. Copy it to a local folder like Documents. Open it with File, Open & Export, Open Outlook Data File.

OST files renamed to PST always fail. OST and PST are different formats, so renaming does not convert them. Open OST files through their own Outlook profile, or export data first.

How to repair a PST that is not an Outlook data file with ScanPST?

Run ScanPST.exe, Microsoft's Inbox Repair Tool, which installs with classic Outlook. It fixes minor structural errors and saves a backup copy before repair. Many guides send you to wrong folders, so match your install type to find it:

Microsoft's repair page lists (x86) root\Office16 for Outlook 2016 and 2019. Users on Microsoft Q&A report finding no ScanPST there on Microsoft 365 and finding it under C:\Program Files instead. When neither folder has it, search drive C: for scanpst.exe.

1. Close Outlook and open your ScanPST folder.
2. Run SCANPST.EXE, select Browse and choose your .pst file.
3. Select Start. Wait until scanning ends.
4. If errors appear, keep backup ticked and select Repair.
5. Start Outlook and open your repaired file.

Run ScanPST again if errors remain. That sequence fixes many PST errors with no extra software. Microsoft says some files need several passes, and items deleted for good or damaged past repair do not return. Check your Lost and Found folder after repair. One Microsoft Q&A user reported missing subfolders after repair, so keep your backup copy until mail checks out.

What to do when ScanPST does not recognize your PST?

ScanPST says it does not recognize your file when its header is broken or your file is not PST. Test your header bytes first. Real PST files start with characters !BDN, which is hex 21 42 44 4E. Run that command in PowerShell with your own path:

Format-Hex -Path "C:\Users\you\Documents\old.pst" -Count 4

You see 21 42 44 4E when your header is intact. Any other bytes mean damage at file start, or another file type under PST name. Then try these steps:

• Restore an older copy from backup, File History or cloud storage.
• Check whether your file is really OST data. In one 2007-era forum thread, a user whose PST failed in ScanPST renamed it to .ost, repaired it with ScanOST, renamed it back and recovered mail. Try it on copies only.
• Use a PST repair tool, which rebuilds files ScanPST rejects. Our guide to repair PST file without ScanPST tool covers that path.

How to fix an oversized PST file?

PST files past their limit turn unstable and trigger errors. Limits depend on file type and Outlook version:

Microsoft sets ANSI files near 1.93 GB and caps them at 2 GB whatever registry values say. Past a warning level, Outlook blocks sending, copying and moving new items. Split old folders into a second PST file or archive them to fix an oversized PST. Our guide to reduce Outlook mailbox size shows how, and Outlook mailbox is full covers warning messages.

How to fix PST is not an Outlook data file when nothing works?

Work down that list when quick checks and ScanPST fail. Every step targets one cause.

1. Check your disk. Failing drives corrupt files again. Open Command Prompt as administrator and run chkdsk C: /f /r on drives that hold your PST. Repair your PST again once it finishes.
2. Start Outlook in Safe Mode. Run outlook.exe /safe. If it disappears, turn off add-ins in File, Options, Add-ins, COM Add-ins, Go.
3. Update Outlook. Select File, Office Account, Update Options, Update Now.
4. Repair Office. Open Settings, Apps, select Microsoft 365 or Office, then Modify and Quick Repair.
5. Create a new profile. Open Control Panel, Mail, Show Profiles, Add, set it as default and attach your PST. One university service desk lists that reset for staff who hit it at first launch. Old profiles stay, so you lose nothing.
6. Check antivirus. Pause real-time scanning for one test, because security software can lock PST files while it scans.

If Outlook reports disabled data file usage, see Outlook data file usage is disabled error. If Import and Export option is missing, see Import Export option greyed out in Outlook.

Does new Outlook support PST files?

New Outlook for Windows does not mount live PST files, and it has no ScanPST. Microsoft added PST import to new Outlook in March 2026, so you can bring mail from PST files into your mailbox. Microsoft says more PST features are coming. See Microsoft 365 Message Center post RM485739 for rollout notes.

Repair steps here apply to classic Outlook. If you see it in new Outlook, switch to classic Outlook or open your PST in tools that read PST files directly.

Steps to open PST files that are not an Outlook data file

1. Install Corbett PST File Converter on a Windows PC and start it. You do not need Outlook.
2. Select Email Data Files, choose PST File and add your .pst file.
3. Preview folders, attachments and message content before you export.
4. Select Export and choose PDF, EML, MBOX, HTML, TXT or CSV.
5. Set date, sender, subject or size filters if needed, then select Save.

It converts mail, contacts and calendars and keeps folder structure with exact read and unread counts. It has no repair feature, so run ScanPST first on damaged files. Need safe copies first? See save Outlook 365 emails to hard drive.

Moving mail into another account from backup files? Corbett Email Recovery Software restores PST backups into Gmail, Microsoft 365 or IMAP mailboxes, but it does not repair corrupt files either.

Which fix matches your cause?

Match what you see to your fix, then start at that row.

How to stop PST errors from coming back?

• Prevent PST errors by keeping every live PST on a local drive and out of OneDrive, network shares and USB sticks.
• Close Outlook before you copy, move or back up PST files.
• Keep dated backup copies of every PST you cannot lose.
• Split any PST near 40 GB into yearly files.
• Run chkdsk when Outlook closes unexpectedly twice, before errors repeat.
• Keep Outlook updated so every build opens all PST versions.

Questions about PST is not an Outlook data file