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What a PST file is and why it stops opening
A PST (Personal Storage Table) is an Outlook data file stored locally on a Windows computer. It can contain mail, calendar entries, contacts, tasks and folders that Outlook opens through a profile. Corruption affects the file’s internal structure, so Outlook may refuse to open it, show an error when a folder is selected, or display incomplete folders and messages.
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A repair can restore the file’s structure, but it is not a guarantee that every item will return. Microsoft explains that Inbox Repair may need several runs and cannot recover data that was permanently deleted or damaged beyond repair. If a structural block cannot be read, the tool may remove that block; items stored there can disappear.
Protect the original before changing anything
Do these checks before launching the repair tool:
- Exit Outlook completely. A PST that is still open by Outlook or another process should not be repaired.
- Find the PST in Windows File Explorer and make a separate copy on another local drive or folder. Keep the original untouched while you test the copy.
- Use enough free disk space for the copy, the repaired file and the backup that ScanPST creates.
- Record the PST’s current name and location so you can identify the correct file when several data files are listed.
Microsoft recommends backing up the existing Outlook data file before using Inbox Repair. The repair process normally creates its own backup with the original base name and a .bak extension, but that backup is not a substitute for your separate copy.
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Run Microsoft’s Inbox Repair Tool (SCANPST.EXE)
1. Close Outlook and open ScanPST
Open Windows Search and type SCANPST.EXE. The executable is installed with Outlook or Office, but its exact folder varies by Outlook version, installation type, language and whether Office is 32-bit or 64-bit. If search does not find it, search the Office installation folders for the same filename. Open the executable after Outlook has closed.
2. Select the damaged PST
- In Inbox Repair Tool, select Browse.
- Select the damaged file whose name ends in
.pst. - Select Start to let ScanPST analyze the file.
The first pass is a diagnostic scan. It reports whether structural errors were found; it does not change the PST until you choose the repair command.
3. Repair the reported errors
If ScanPST reports errors, select Repair. When the dialog asks where to save the backup, use a clearly identified location and retain the .bak file. Do not overwrite your separate safety copy. The tool may take time on a large PST or one with extensive damage.
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4. Repeat the scan when necessary
Microsoft says ScanPST may need to be run several times. After a repair finishes, run the tool against the repaired PST again and repeat the scan-and-repair cycle while it continues to find new structural errors. Stop when a pass reports no additional errors or reaches a steady result.
For Outlook 2016 version 1807 and later, Microsoft documents a command-line multi-pass mode. The -rescan option repeats scans until a steady state is reached. Its default is 10 passes and the documented maximum is 20. This automatic multi-pass mode does not support PST files stored on a network share; use a local copy instead. Older Outlook versions use the legacy single-pass behavior, so you must reopen the tool for each additional scan.
Open the repaired file and check what was recovered
Start Outlook with the profile that normally uses the PST. Open the folders that previously failed and test several messages, calendar items and contacts. A successful repair can leave some items in a different folder because the original folder structure was damaged.
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Recovered Personal Folders
Outlook may create a folder named Recovered Personal Folders. Expand it and compare its contents with the folders you expected. Move intact items into an organized PST only after you have finished checking the repaired file.
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If ScanPST cannot place recovered items back into their original folders, Microsoft says they may appear under Lost and Found. Inspect this folder carefully; it can contain messages or other items whose original locations are no longer known.
Use the ScanPST backup to look for additional items
The .bak created during repair can contain content that was not placed in the repaired PST. Preserve the original backup and work only on a copy:
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- Copy the
.bakfile to a separate working folder. - Rename the copied file so its name ends in
.bak.pst. - Create a new, empty PST in Outlook.
- Import the renamed copy into that new PST and inspect the imported folders and items.
Keep the untouched .bak in case another recovery attempt is needed. Do not repeatedly rename or repair the only backup.
Create a new PST when the repaired file remains unreliable
A repaired file that still produces errors should not remain your working archive. Create a new PST, then move or import the folders and messages that open correctly from the repaired file, its recovered folders and the copied .bak.pst. This gives the recovered items a clean container while preserving the damaged file for reference.
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Know what ScanPST cannot recover
- Permanently deleted items: Inbox Repair is not an undelete tool. Items that were permanently deleted may not be recoverable.
- Unreadable structural blocks: If a block cannot be read, ScanPST may remove it so the rest of the file can open. Items stored in that block can be lost.
- Every error in one pass: A clean result is not guaranteed on the first run; Microsoft documents repeated runs for persistent structural problems.
- Data that never existed in the file: Repair can only work with content still present in the PST or its backup.
PST versus OST: use the right recovery method
| File type | What it contains | Typical repair path | Important limitation |
|---|---|---|---|
| PST | A local Outlook data file that users commonly open or import. | Back up the file, run SCANPST.EXE, repeat scans if needed, then create a new PST and import recovered items. |
ScanPST may remove unreadable blocks, and permanently deleted or severely corrupted items may not return. |
| OST | An offline copy synchronized with an Exchange mailbox. | Inbox Repair does not analyze the Exchange mailbox. If the offline OST is damaged, delete the OST so Outlook can recreate it the next time Outlook opens. | The mailbox is the authoritative Exchange data store; the OST is its offline copy. |
Do not apply PST instructions blindly to an Exchange OST. ScanPST is intended for local Outlook data files and does not repair data stored in the Exchange mailbox itself.
Choose the safest recovery approach
| Situation | Best next step | Why |
|---|---|---|
| The PST will not open or Outlook reports structural errors | Work on a copy with ScanPST, then select Repair. | Inbox Repair is Microsoft’s first-line method for a damaged local PST. |
| The first repair still reports errors | Run ScanPST again; use the documented -rescan mode when supported. |
Microsoft says multiple passes may be required; Outlook 2016 version 1807 and later support automatic rescans. |
| The file opens but folders or messages are missing | Inspect Recovered Personal Folders and Lost and Found, then examine a copied .bak.pst. |
Recovered items may not fit the original structure, and the backup may contain additional content. |
| The repaired PST remains unstable | Create a new PST and import or move intact items into it. | A clean container avoids continuing to depend on a damaged structure. |
| An Exchange OST is damaged | Do not run PST repair; remove the offline OST and let Outlook recreate it. | OST data is synchronized with the Exchange mailbox, and ScanPST does not analyze mailbox data. |
Troubleshooting common outcomes
ScanPST cannot find the file
Use Browse inside the tool and select the actual .pst path from File Explorer. If several PSTs exist, check the filename and size before selecting one. Search for SCANPST.EXE separately; its installation path changes with Office edition, architecture and language.
Outlook still shows an error after repair
Close Outlook, run another scan against the repaired copy and check whether the error count changes. If the file opens only intermittently, stop using it as the primary archive and build a new PST from the folders that remain readable. Keep the original and the .bak for further inspection.
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Folders are present but messages are missing
Check Recovered Personal Folders and Lost and Found before assuming the messages are gone. Then import the copied .bak.pst into a new PST and compare the results. A missing item may have been stored in an unreadable structural block, in which case ScanPST cannot guarantee recovery.
The PST is on a network location
Copy the file to a local drive before using the automatic multi-pass mode. Microsoft’s documented -rescan mode does not support networked PST files. Preserve the network copy as the untouched source and repair the local working copy.
After recovery: make the new PST your working file
- Open the new PST in the Outlook profile and confirm that its main folders load normally.
- Open representative messages and verify attachments, dates and senders before deleting anything.
- Leave the original PST and repair backup untouched until your checks are complete.
- If the data came from an Exchange account, treat the mailbox and recreated OST separately from any local PST archive.
Repair is a process of preserving what can still be read, not a promise to reconstruct every damaged record. The safest sequence is always: copy first, scan, repair, inspect recovered folders, test the backup, and move verified items into a new PST when the original remains questionable.
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