“The Outlook data file cannot be accessed”: causes and fixes

Two messages mean Outlook could not use a .pst file:

• The file … .pst cannot be accessed (or cannot be opened), and
• The file … .pst is not an Outlook data file (.pst).

The cause is often simple: the file is in use, read-only, or on a drive Outlook does not handle well. Only sometimes is the file damaged. Work through these in order.

1. Another program has the file open

Only one program can use a PST at a time. Close Outlook completely (check the system tray), and pause backup and sync tools (OneDrive, Dropbox, backup software) that may be reading the file. Then open it again.

2. The file is on a network drive, USB stick or synced folder

Outlook expects PST files on a local disk. Over a network, on removable drives or inside a syncing folder, the file can be locked or changed mid-write. Copy the PST to a local folder such as Documents\Outlook Files and open the copy.

3. Permissions or read-only

Right-click the file › Properties: clear Read-only, and on the Security tab check that your account may modify it. Files restored from CDs, old backups or another user’s profile are often read-only.

4. It is not a PST

Backups sometimes contain other files renamed or mistaken for PSTs: an .ost (an offline copy of a server mailbox), an .olm (Outlook for Mac), or a ZIP. Our PST Viewer tells you immediately if the file is not a PST. An OST can be turned into a PST with OST to PST.

5. The file is old or very large

Files from Outlook 97–2002 use the old ANSI format, which stops working at 2 GB and is not opened by every tool. Newer Unicode PST files have a default size limit of 50 GB in Outlook 2010 and later. A file near or over these limits is a candidate for damage; see PST file too large.

6. The file is damaged

If none of the above helps, the PST itself is probably damaged: a crash or power cut while Outlook was writing, a failing disk, or a broken sync. Two ways forward:

• SCANPST (the Inbox Repair Tool) comes with Outlook and repairs the file in place. Work on a copy: see our SCANPST guide.
• Our Repair PST page runs a free health check that shows what is damaged and how many messages can be recovered, then copies everything readable into a new PST. The original is never changed, and anything that cannot be saved is listed in the report.

Frequently asked

Is my mail lost? Usually not. Damage typically affects some internal structures or a few messages; the rest of the mail is still in the file.

Should I keep trying to open the file in Outlook? No. Make a copy first, and work on the copy, so nothing makes the damage worse.