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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallScanPST.exe is Microsoft Outlook’s Inbox Repair Tool. It diagnoses and repairs structural errors in local Outlook data files, primarily PST files, and can also inspect an offline OST file. To use it safely, close Outlook, back up the original file, run ScanPST against the correct file, repair the errors it reports, and repeat the scan if necessary. It cannot repair every permanently deleted or severely damaged item, and it does not analyze data that remains in an Exchange mailbox.
What ScanPST.exe does
Microsoft describes ScanPST.exe as a utility that can “diagnose and repair errors in your Outlook data file.” It works on the internal structures of a local Outlook data file rather than on Outlook’s user interface or on the mail server itself.
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A PST (Personal Storage Table) normally holds locally stored mail, calendar entries, contacts, tasks and other Outlook items. An OST (Offline Storage Table) is an offline copy associated with an Exchange, Microsoft 365 or similar account. The distinction matters because a damaged local file and a synchronization problem are different problems.
During a scan, the tool validates structures such as B-trees and reference counts inside the file. If a block cannot be read, ScanPST may remove that block and, with it, the Outlook item that depended on it. The event is recorded in the ScanPST log. Repair therefore means correcting a file structure, not guaranteeing restoration of every message or folder.
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Decide whether ScanPST is the right fix
| Situation | Use ScanPST? | Reason |
|---|---|---|
| Outlook reports that a PST is damaged or cannot be opened | Yes | ScanPST is intended to diagnose and repair errors in local Outlook data files. |
| Mail in an Exchange mailbox is missing or synchronization is failing | Not as a first step | Microsoft says the tool does not connect to or analyze data stored in an Exchange mailbox. |
| An offline OST is damaged | Sometimes, but rebuilding is often the cleaner path | Outlook can recreate an offline OST after it is deleted and Outlook is opened again with the account. |
| Items were permanently deleted long ago | Do not assume recovery | Microsoft warns that permanently deleted or irreparably corrupted items may not be recovered. |
| ScanPST itself will not open | No, not until Office is repaired | Microsoft’s guidance is to repair the Office installation when the utility will not start. |
Use the table as a triage guide. If the same account works in webmail or on another device while only the local Outlook copy fails, the problem is more likely local. If the mailbox is wrong everywhere, repairing a local file will not correct the server-side issue.
Prepare safely before scanning
1. Exit Outlook completely
Close every Outlook window before you browse to ScanPST or select a data file. Outlook can keep the PST or OST open after its main window disappears, so wait for the process to close before proceeding. Do not scan a file that Outlook is actively using.
2. Identify the data file
Confirm whether the failing file is a PST or an OST and note its full name and location. In Outlook, the data-file list is available from File > Account Settings > Account Settings > Data Files; the labels can vary slightly between Outlook editions. If Outlook cannot open, use the file that your profile or previous backup identifies rather than choosing a similarly named file at random.
3. Make a working backup
Copy the original PST or OST to a separate, safe location before starting. Keep the untouched copy until you have verified the repaired result. Microsoft recommends a backup, and ScanPST also creates a repair backup as part of the repair process. Those are different protections: your manual copy gives you an independent original, while the utility’s backup is generated during its own operation.
Do not overwrite your only copy with an experimental repair. If the scan removes unreadable blocks, the independent copy is the safest way to retry with different choices or seek specialist help.
Find the correct ScanPST.exe
The executable is installed with Microsoft Office or Outlook; it is not normally a separate download. Microsoft lists representative Office 16 locations such as:
C:Program FilesMicrosoft OfficerootOffice16C:Program Files (x86)Microsoft OfficerootOffice16
Your path can differ with the Outlook version, 32-bit versus 64-bit Office, Click-to-Run versus another installation type, and the drive on which Office is installed. The folder name also changes for other Office generations.
If those locations do not contain the file, search Windows for SCANPST.EXE after Office has been installed. Check that the result belongs to the Microsoft Office or Outlook installation you actually use. If several copies appear, use the one associated with the current installation rather than an old copy left by an earlier Office version.
Run a standard PST repair
Perform the following sequence with Outlook closed and your backup already made.
- Open
SCANPST.EXE. - Choose Browse and select the PST you identified in your Outlook profile.
- Press Start to let the tool analyze the file.
- Read the scan result. If errors are reported, select Repair.
- Allow the repair to finish without closing the utility or interrupting the disk.
- Open Outlook with the profile that uses the repaired file.
The first scan can report errors without immediately changing the file. The repair stage is the operation that writes corrected structures. Keep the repair backup and your separate original until Outlook has been checked.
Check Outlook after the repair
Open the profile associated with the repaired PST and test the areas that previously failed: the Inbox, custom folders, calendar, contacts, search and the ability to send or save a message. A successful launch does not prove that every item is intact; inspect the folders that matter to you.
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If Outlook cannot restore the original folder tree, look for a folder named Recovered Personal Folders or Lost and Found. Microsoft notes that recovered content can appear there and that some recreated folders may be empty. Move verified items into the correct folders only after you have confirmed that they open normally.
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Review the ScanPST log as well. It can identify blocks that were removed because they were unreadable. A missing item mentioned in the log may not be recoverable by running the same repair again.
Run more than one pass when errors remain
Microsoft states that the Inbox Repair Tool may need to be run several times to fully repair a PST. After the first repair, close Outlook again, make sure the file is no longer in use, and scan the repaired copy. If errors remain, run the repair again and then retest Outlook.
Repeated passes should be deliberate rather than endless. Compare each scan result and keep the repair log. Always preserve the untouched original so that a later pass cannot become your only version.
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Outlook 2016 version 1807, build 16.0.10325.20082, and later support command-line multi-pass operation. The process can continue until the scan reaches zero errors or produces two identical consecutive results. This version/build detail describes when the behavior was introduced; it is not a repair-success statistic.
Command-line switches vary with the installed Office build and the location of the executable. Use Microsoft’s instructions for the syntax that matches your installation rather than copying a switch intended for another build. The same safety rules apply: close Outlook, work from a backup, and retain the logs.
Understand what a repair can and cannot recover
Structural corrections
ScanPST is designed to correct internal consistency problems. It checks indexes, references and other structures that allow Outlook to locate items inside a PST. When those structures are repaired, Outlook may become able to open the file or display folders that previously generated an error.
Unreadable blocks
If a section of the file cannot be read, the utility may remove it so that the remaining structure is usable. The associated message, appointment or other item can disappear. The log is important because it records this kind of loss instead of silently promising a complete restoration.
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Microsoft warns that ScanPST cannot recover every item. Permanently deleted content and data that is too badly corrupted may be beyond the tool’s ability to reconstruct. Do not interpret a repaired file as proof that deleted mail has been restored.
What to do with an OST file
An OST is an offline representation of an account whose authoritative data is normally held by the mail service. ScanPST can be pointed at an OST file, but it does not connect to or analyze the Exchange mailbox itself. Repairing an offline cache therefore cannot fix a server-side mailbox problem.
When rebuilding is appropriate
If the account is an Exchange account and the offline OST is the damaged component, deleting the offline OST allows Outlook to recreate it the next time Outlook opens. Before deleting anything, confirm that needed data has synchronized to the server and that the account is available online. Any item that existed only in the damaged offline file can be lost when the cache is removed.
When not to delete the OST
Do not treat deletion as a universal fix. If the mailbox has not synchronized, the server is unavailable, or the OST contains unsent or otherwise local-only data, first preserve the file and resolve synchronization questions. ScanPST cannot supply a copy of data that never reached the mailbox.
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If ScanPST will not start
A missing window, immediate crash or error when opening the utility points to an Office installation problem rather than a PST problem. Microsoft suggests repairing the Office application. Use the Windows repair option for the installed Office or Microsoft 365 package, then restart Windows and try ScanPST again.
The exact repair controls depend on Windows and Office edition. Choose the repair action for the installation that contains Outlook, not an unrelated application. If Office repair does not restore the utility, preserve the data-file backup and use Microsoft support or an administrator who can identify the installed build.
Troubleshoot common results
Outlook still reports that the file is corrupt
- Confirm that Outlook was closed before the scan and that you selected the same file used by the profile.
- Run another scan-and-repair pass; several passes may be required.
- Open the repaired copy only after the utility has finished.
- If the file remains unusable, work from the untouched backup rather than repeatedly modifying the only original.
Outlook opens, but folders or messages are missing
- Check Recovered Personal Folders and Lost and Found.
- Read the ScanPST log for removed or unreadable blocks.
- Compare the repaired file with your backup before moving or deleting anything.
- Remember that permanently deleted or irreparably corrupted items may not be recoverable.
The repair appears to finish but synchronization is still wrong
Determine whether you repaired a local cache while the real fault is in the Exchange account or mailbox connection. ScanPST does not inspect server-side Exchange data. Test the account through its web interface or another trusted client; if the mailbox is wrong there too, pursue an account or service-side remedy instead of more PST repairs.
A second pass reports the same errors
Record the identical result in the log and avoid assuming that unlimited repetitions will restore more data. The documented multi-pass behavior for supported Outlook 2016 builds stops at zero errors or two identical consecutive results. For other builds, repeated manual passes should be limited to what the logs and your backup strategy justify.
Keep a repaired file usable
Once Outlook opens normally, verify the folders and items that are important to you and create a fresh backup of the repaired file. Keep the pre-repair original separately until you are confident that the repaired copy contains what you need. A repair changes file structures; it does not replace a regular backup strategy.
For future failures, record which Outlook profile uses each data file, distinguish PST archives from OST caches, and keep copies where a disk failure or accidental overwrite cannot affect both versions. These simple records make it easier to select the correct file the next time ScanPST is needed.
Manual repair versus an OST rebuild
| Approach | Best fit | Preserves | Main limitation |
|---|---|---|---|
| ScanPST on a PST | Local PST structure errors | Readable structures and items that can be indexed again | Unreadable blocks, permanently deleted items and severe corruption may remain lost. |
| ScanPST on an OST | Problems limited to the offline file structure | Whatever can be read from the local cache | It does not analyze the Exchange mailbox or correct server-side synchronization. |
| Delete and recreate an Exchange OST | A damaged offline cache when the mailbox is safely synchronized | Data that already exists on the server | Unsynchronized or local-only data can be lost. |
The safest choice follows the data’s source. Repair a local PST when the PST is the authoritative copy; rebuild an OST only when the mailbox is authoritative and synchronization has been verified.
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