Outlook PST file lost or corrupted? What to do

Outlook will not open, or it says your data file cannot be accessed, and years of email seem to have gone with it. Sometimes the computer holding the mail has failed altogether. Before you repair or delete anything, work out where your mail really lives. For many people it is safe on a mail server and only the local copy is damaged. For others the file on the disk is the only copy that exists, and that changes what you should do next. The steps here apply to classic Outlook for Windows.

PST or OST: which do you have?

Outlook keeps mail in one of two kinds of file, and they behave very differently.

• OST (offline data file): a local cached copy of a mailbox held on a server. Microsoft 365, Exchange, Outlook.com and most IMAP accounts work this way. It usually sits in C:\Users\yourname\AppData\Local\Microsoft\Outlook.
• PST (Outlook data file): a standalone file. POP accounts, archives and exported mail use it, and the file itself is the mail. It is commonly found in Documents\Outlook Files, though older setups and archives may be elsewhere.

To check, open File, Account Settings, then Account Settings again and choose the Data Files tab. If Outlook will not start, open the Mail icon in Control Panel and choose Data Files there.

Common signs of trouble

• “Outlook data file cannot be accessed”
• “The file is not an Outlook data file (.pst)”
• “Errors have been detected in the file”
• a message saying the .pst file could not be found
• Outlook hanging on the loading profile screen
• folders that are suddenly empty, or an archive that has vanished from the folder list

Typical causes are Outlook or Windows being shut down abruptly, a power cut during a write, a PST kept on a USB stick or network share, and bad sectors on a failing drive. If your computer has also become slow, noisy or prone to freezing, assume that the drive is part of the problem.

If it is an OST file

When your mailbox is still active on the server, this is usually good news. Sign in to webmail, such as outlook.office.com for Microsoft 365. If your mail is there, it is safe. Outlook can build a new OST by downloading it again, normally by creating a new mail profile. Rename the old OST rather than deleting it until you have confirmed everything has returned.

For anything deleted from the mailbox, look in Deleted Items, then use Recover Deleted Items. On Microsoft 365 these items are kept for a limited period, 14 days by default, so check soon. Your IT administrator may be able to help if you use a work account.

An OST becomes much more important if the server copy has gone, for example because an account was closed or the mail provider has changed. It may then be the only copy of the mail, and it cannot simply be opened in Outlook on another computer. Keep the file, do not let Outlook recreate over it, and ask for advice.

If it is a PST file

Treat a PST as an original. Before running anything, close Outlook and copy the file to a different drive. If the copy fails or stalls, stop there, as this suggests a problem with the disk rather than the file.

If the copy succeeds, Microsoft’s Inbox Repair Tool, SCANPST.EXE, can often fix a damaged file. You will find it in your Office program folder, typically C:\Program Files\Microsoft Office\root\Office16. Run it against the copy, not the original. Be aware of its limits:

• It may remove anything it cannot repair, so some items can disappear.
• Rescued items may appear in a Recovered Personal Folders or Lost and Found folder.
• Very badly damaged files may fail altogether, and repeat runs rarely help.

If you have kept the untouched original, a failed repair costs you nothing, because you can still try other options.

If the PST was deleted

Check the Recycle Bin, then search the whole computer for *.pst, as old copies often sit in forgotten folders. Check backups, File History and old computers too. If it really has been deleted, stop using the computer as soon as you can, because normal activity can overwrite the space it occupied. PST files tend to be large, so they are especially vulnerable to partial overwriting. On SSDs, deleted data is often cleared by the drive itself soon afterwards, so the chances are lower.

If the drive has failed

When the laptop will not boot, the drive is clicking or Windows cannot see it, leave the file alone and shut the machine down. Avoid reinstalling Windows and avoid Reset this PC, as both can overwrite mail files. Recovery software is also a poor choice for a struggling drive, because scanning puts it under heavy load.

The safe approach is to copy the drive first, then extract the mail file from the copy. Once the file is out, damage can be dealt with separately. See our laptop data recovery page, or request a quote online.

Protect your mail in future

Archive PST files are easy to forget, and they are often missed by cloud sync and backup tools. Keep them on a local drive rather than a USB stick or network share, include them in your backups and close Outlook before they run. An archive that exists only on one laptop is a single point of failure, so keep a second copy somewhere else.

Lost important email?

Call Data Retrieval on 020 7064 4996. We offer a free assessment with no obligation, so you will know where you stand before any work is done.