How to Convert a Corrupted PST File

The Problem: Your PST File Is Damaged

PST file corruption is one of the most common and frustrating Outlook problems. You try to open a PST file and Outlook displays an error like “The file is not a personal folders file,” “Errors have been detected in the file,” or simply crashes. The file might be partially readable but missing messages, or it might be completely inaccessible.

Corruption can strike PST files of any size or age, and the data inside — years of email correspondence, critical business communications, important attachments — may seem lost.

What Causes PST Corruption

Understanding the causes helps prevent future corruption and informs the recovery approach:

• Oversized files — ANSI PST files (Outlook 2002 and earlier) have a hard 2 GB limit. Approaching or exceeding this limit causes structural damage. Even Unicode PST files degrade in performance and stability above 10 GB.
• Improper shutdown — if Outlook is force-closed, the computer loses power, or the operating system crashes while Outlook is writing to the PST file, internal data structures can be left in an inconsistent state.
• Storage media problems — bad sectors on a hard drive, failing SSD controllers, or corruption during file transfer (network drives, USB) can damage any portion of the file.
• Virus or malware — some malware specifically targets Outlook data files.
• Network storage — storing PST files on network drives (NAS, shared folders) is explicitly unsupported by Microsoft because file locking mechanisms over a network are unreliable. This is one of the most common causes of PST corruption.
• Concurrent access — multiple applications or Outlook instances accessing the same PST simultaneously can cause write conflicts.

Solution: Repair and Convert

Step 1: Try Microsoft’s ScanPST.exe (Inbox Repair Tool)

Microsoft includes a free repair utility with every Outlook installation:

• Outlook 2019/365: C:\Program Files\Microsoft Office\root\Office16\SCANPST.EXE
• Outlook 2016: C:\Program Files (x86)\Microsoft Office\Office16\SCANPST.EXE
• Outlook 2013: C:\Program Files (x86)\Microsoft Office\Office15\SCANPST.EXE

How to use it:

1. Close Outlook completely.
2. Run SCANPST.EXE and browse to the damaged PST file.
3. Click Start to scan for errors.
4. If errors are found, check “Make backup of scanned file before repairing” and click Repair.
5. Run it multiple times — ScanPST often requires 3-5 passes to fix all issues.
6. Open the repaired file in Outlook to check if the data is accessible.

ScanPST is effective for minor corruption (damaged B-tree entries, orphaned nodes) but cannot recover files with severe structural damage.

Step 2: Convert the Corrupted or Repaired PST With MailtoPst

Whether ScanPST fully repaired the file or only partially fixed it, converting with MailtoPst is the next step:

1. Go to mailtopst.com (or choose your preferred target format).
2. Upload the PST file — either the original corrupted file or the ScanPST-repaired version.
3. MailtoPst attempts recovery — the conversion engine has built-in tolerance for common corruption patterns. It reads the PST at a low level and extracts every recoverable message, skipping damaged blocks.
4. Review the output — the conversion report lists any messages that could not be extracted. The successfully converted messages are available in the download.

What MailtoPst Can Recover

• Messages in intact folder structures.
• Messages whose data blocks are undamaged, even if the folder B-tree has errors.
• Attachments linked to recoverable messages.
• Headers and timestamps for all extracted messages.

What May Be Unrecoverable

• Messages whose data blocks are physically overwritten or zeroed out.
• Messages in sections of the file affected by bad sectors.
• Folder names and hierarchy if the Name-to-ID Map is severely damaged.

Prevention: How to Avoid PST Corruption

• Never store PST files on network drives — keep them on local SSDs or hard drives.
• Keep PST files under 10 GB — archive older messages to separate files or convert them to EML for long-term storage.
• Use Unicode format — ensure Outlook creates Unicode PST files (the default since Outlook 2003), not ANSI format.
• Shut down properly — always close Outlook before shutting down or restarting the computer.
• Regular backups — copy PST files to a backup location on a schedule. If corruption strikes, you can revert to a recent backup.
• Use the AutoArchive feature — Outlook’s AutoArchive moves old messages to a separate PST, keeping your primary file lean and less vulnerable.

Why MailtoPst for Corrupted PST Recovery

• Corruption-tolerant parsing — the engine reads around damaged blocks and extracts everything it can, rather than failing on the first error.
• No software to install — upload from any browser, on any OS.
• Multiple output formats — convert to EML (individual files), MBOX (Thunderbird archive), or a clean new PST (for Outlook).
• Secure handling — TLS encryption, EU servers, automatic deletion. GDPR compliant.

Upload your file now and recover what you can. Try free — no credit card required.

Frequently Asked Questions

Can MailtoPst repair a corrupted PST file?

MailtoPst is a conversion tool, not a repair tool. It does not modify the original PST file. Instead, it reads the file in a corruption-tolerant manner and extracts recoverable messages into a new, clean output file. The original PST remains unchanged.

Should I run ScanPST before uploading to MailtoPst?

It is recommended but not required. Running ScanPST first may fix minor issues and make more messages accessible to the conversion engine. However, MailtoPst can also process files that ScanPST could not fully repair.

How much data can I expect to recover from a corrupted PST?

Recovery rates depend on the severity and location of the corruption. Minor corruption (damaged index entries) typically allows 95-100% recovery. Severe physical damage (bad sectors across the file) may result in lower recovery rates. The conversion report details exactly what was and was not recovered.

Is there a risk of making the corruption worse by uploading the file?

No. MailtoPst reads the file in a non-destructive manner. The original file is not modified in any way. Always keep a copy of the original corrupted file as a safeguard.

What if ScanPST.exe cannot find any errors but the file still does not work?

This can happen with certain types of corruption that ScanPST does not detect. Upload the file to MailtoPst — the conversion engine uses different parsing strategies that may succeed where ScanPST failed.

Upload your file now and save your emails from a damaged PST.