0x8004010F and damaged Outlook data files

It is an OST. The mailbox is on the server, so the local copy can be thrown away.

1. Confirm it is an OST and find it.

   PowerShellCopy

   Get-ChildItem "$env:LOCALAPPDATA\Microsoft\Outlook" -Filter *.ost | Format-Table Name,Length,LastWriteTime

2. Check for anything stored only locally first — items in a local folder outside the mailbox, and any PST attached to the same profile. Those are not on the server.

   The OST is safe to delete only for what is genuinely synchronised. A mailbox with local-only folders, or one that has been archiving to the OST, will lose that content — check before, not after.

3. Close Outlook and rename rather than delete the file.

   PowerShellCopy

   Get-Process OUTLOOK -ErrorAction SilentlyContinue | Stop-Process -ForceGet-ChildItem "$env:LOCALAPPDATA\Microsoft\Outlook\*.ost" | Rename-Item -NewName { $_.Name + '.old' }

4. Start Outlook. It builds a new OST and downloads the mailbox. On a large mailbox this takes hours.

5. Once everything is present, delete the .old file to reclaim the space.

It is a PST. This is the only copy of that mail — copy it before doing anything.

1. Close Outlook and copy the PST somewhere else. This copy is the safety net for everything that follows.

   PowerShellCopy

   Copy-Item 'C:\Users\me\Documents\Outlook Files\archive.pst' 'D:\backup\archive-copy.pst'

2. Find the repair tool. It ships with Office and is not on the Start menu.

   PowerShellCopy

   Get-ChildItem 'C:\Program Files\Microsoft Office' -Recurse -Filter SCANPST.EXE -ErrorAction SilentlyContinue | Select-Object -First 1 FullName

3. Run SCANPST.EXE against the file, let it make its own backup when offered, and run it repeatedly until it reports no errors — one pass is frequently not enough.

   The tool fixes what it can see in a single pass and often uncovers more damage underneath. Three or four passes on a badly damaged file is normal, and stopping after one leaves it broken.

4. If a PST is over about 20GB, or lives on a network share or a synced folder such as OneDrive, that is the cause and it will recur. Move it to a local disk.

   Outlook data files are not supported on network shares or sync folders. The access pattern is incompatible with them and corruption is the normal outcome, not bad luck.

5. If the repair cannot complete, a commercial PST recovery tool run against the copy is the next step.