If Outlook says it can’t open your data file, your emails are usually still inside the PST. The file’s internal index is what broke. The right tool rebuilds that index and saves your mail, contacts and calendar into a new, healthy PST.
Microsoft’s free ScanPST fixes minor damage, but it often stalls on large or badly corrupted files. An online PST repair tool is the next step. You upload the file in a browser, preview what can be recovered, and download a repaired copy, with no software to install.
We compared the main options on four things that decide which one you should use: file-size limit, real price, how long they keep your mailbox, and whether you need Outlook installed. Every price and limit below comes from the vendor’s own page as of October 2026.
- Best free option: Stellar Online PST Repair. It repairs one PST up to 500 MB at no cost.
- Best for large files and OST: Recovery Toolbox for Outlook Online. It has no size limit and charges $10 per GB.
- Best if you can’t upload your mailbox: PST Repair Kit. This desktop app repairs the file on your own PC from $39.
- Try first, for free: Microsoft’s ScanPST, which is already installed with Outlook.
Table of Contents
Signs your PST file is corrupted
These Outlook errors usually point to a damaged PST rather than a broken Outlook install:
- “Outlook data file cannot be accessed” (error 0x8004010F)
- “The file outlook.pst is not a personal folders file”
- “Errors have been detected in the file outlook.pst”
- “Cannot start Microsoft Outlook. The set of folders cannot be opened”
- A data error or cyclic redundancy check (CRC) error when opening the file
- Folders that look empty, attachments that won’t open, or Outlook freezing on one folder
Common causes are a power cut or forced shutdown while Outlook was writing to the file, bad sectors on the drive, and a PST stored on a USB drive, network share or synced folder (OneDrive, Dropbox) that disconnected mid-write. Oversized files are another cause. Old ANSI-format PSTs from Outlook 2002 and earlier break near 2 GB, and modern Unicode PSTs slow down and get unstable as they approach Outlook’s default 50 GB limit.
Whatever the cause, do one thing before anything else: copy the PST to a healthy local drive and work only on the copy.
Step 0: Try ScanPST (free) first
ScanPST.exe, also called the Inbox Repair Tool, ships with desktop Outlook and fixes minor index damage at no cost. Microsoft notes you may need to run it several times. Be aware that it repairs the file in place and can drop items it can’t read, so run it on a copy.
Where to find it (64-bit Windows with 32-bit Office; with 64-bit Office, drop the ” (x86)“):
| Outlook version | Folder |
| Microsoft 365, 2024, 2021, 2019, 2016 | C:\Program Files (x86)\Microsoft Office\root\Office16 |
| Outlook 2013 | C:\Program Files (x86)\Microsoft Office\Office15 |
| Outlook 2010 | C:\Program Files (x86)\Microsoft Office\Office14 |
| Outlook 2007 | C:\Program Files (x86)\Microsoft Office\Office12 |
How to run it
- Close Outlook completely.
- Open SCANPST.EXE from the folder above.
- Select Browse and pick your PST. To find its path, open Outlook and go to File > Account Settings > Account Settings > Data Files.
- Select Start. If errors are found, keep “Make backup of scanned file before repairing” ticked and select Repair.
- Run it again until it reports no errors, then open Outlook. Check the Recovered Personal Folders or Lost and Found folder for items it moved.
Move on to a repair tool if ScanPST freezes, says it doesn’t recognise the file, reports a fatal error, or finishes but your folders are still empty. Use the backup copy, not the file ScanPST already changed.
Source: Microsoft Support, Repair Outlook Data Files.
The 3 best online PST repair tools
1. Stellar Online PST Repair: best free option
Stellar Online PST Repair is the only tool here that repairs a file completely free, as long as it is 500 MB or smaller. You sign in, upload the PST, and the service repairs it in an automated environment. Stellar says most files are done within 15 minutes.
What stands out
- Free repair of one PST up to 500 MB, with no credit card
- Preview of the recovered folder tree and item counts before you download
- Recovers emails, attachments, contacts, calendar, tasks, notes and journal entries
- Handles password-protected PSTs and both ANSI and Unicode formats (Outlook 2003 to 2021)
- No Outlook needed for the repair itself
Pricing: Free up to 500 MB. Files from 500 MB to 5 GB cost $29.99 each. Above 5 GB, you need the $79.99 Stellar Repair for Outlook desktop edition, which has no size limit and works offline.
Privacy: Free-plan files are deleted after 24 hours and Premium files after 48 hours.
Limitations: One file per purchase, a hard 5 GB cap online, and the listed version support stops at Outlook 2021.
Best for: A single PST under 500 MB, or anyone who wants to see what’s recoverable before paying.
2. Recovery Toolbox for Outlook Online: best for large files and OST
Recovery Toolbox for Outlook Online has no file-size limit and accepts both PST and OST files, which makes it the pick for big archives. You choose the file, enter your email address, and wait for the analysis. There’s no account to create.
What stands out
- No size limit on uploaded PST or OST files
- Free preview of the folder tree, plus a free demo PST containing five items from each folder
- Reads password-protected and encrypted files without the password
- Outputs a new Unicode PST that opens in Outlook 2010 to 2024 and Outlook for Microsoft 365
- Works in any browser, so you can run it from a Mac, tablet or phone
Pricing: $10 per GB of the original file, paid only after you’ve seen the preview. A desktop version for Windows costs $39 (personal), $59 (business) or $99 (site licence).
Privacy: Files are kept on the server for 30 days before automatic deletion. That is much longer than Stellar’s window, so use the desktop version for confidential mail.
Limitations: Per-GB pricing gets expensive for very large files compared with a one-off desktop licence. The desktop app needs Outlook installed to save a PST.
Best for: PST files over 5 GB, orphaned OST files from an old Exchange or Microsoft 365 profile, and anyone without a Windows PC to hand.
3. PST Repair Kit: best offline alternative
PST Repair Kit (sold as PST Repair Set) is not an online service. It’s a small Windows download that repairs the PST on your own computer. We include it because many people searching for an online tool really need a fix that never uploads their mailbox.
What stands out
- Repairs on your PC, so your mail never leaves it
- Three modes: recovery, OST-to-PST conversion, and a scan for deleted items
- Splits the output PST into parts of any size you choose, useful for oversized archives
- Exports to separate EML, MSG, VCF and text files if you don’t want a PST
- Opens password-protected files, and supports both ANSI and Unicode PSTs
- Free demo with a preview of recoverable items
Pricing: $39 (personal), $59 (business) or $99 (site licence). Licences are per computer (the site licence covers one location), not per file.
Limitations: Windows only, and Microsoft Outlook must be installed. Refunds require evaluating the demo first. Its terms are governed by Russian law, which some companies’ procurement rules won’t accept.
Best for: Confidential or regulated mailboxes, IT staff repairing many PSTs, and files too large to upload.
Comparison: online PST repair tools side by side
| Stellar Online PST Repair | Recovery Toolbox Online | PST Repair Kit | |
| Type | Online (desktop edition available) | Online (desktop edition available) | Desktop only (Windows) |
| Free tier | Full repair up to 500 MB | Preview + demo PST (5 items per folder) | Demo with preview |
| Paid price | $29.99 per file (to 5 GB); $79.99 desktop | $10 per GB; $39 / $59 / $99 desktop | $39 / $59 / $99 |
| Online size limit | 5 GB | None | Not applicable |
| OST files | Not listed | Yes | Yes, plus OST-to-PST conversion |
| Outlook needed | No | No (online) | Yes |
| Files kept on server | 24 h (free), 48 h (paid) | 30 days | Never uploaded |
| Works on Mac / mobile | Yes, any modern browser | Yes, any browser | No |
What it actually costs, by file size
The cheapest tool changes with the size of your PST. Prices below use each vendor’s list price. For Recovery Toolbox we assume a part-gigabyte is billed as a full one, so check the exact quote on its preview page.
| PST size | Stellar | Recovery Toolbox Online | PST Repair Kit | Cheapest |
| 300 MB | Free | $10 | $39 | Stellar |
| 2 GB | $29.99 | $20 | $39 | Recovery Toolbox |
| 5 GB | $29.99 | $50 | $39 | Stellar |
| 12 GB | $79.99 (desktop) | $120 | $39 | PST Repair Kit |
| 30 GB | $79.99 (desktop) | $300 | $39 | PST Repair Kit |
In short: online repair is cheapest up to about 5 GB. Above that, a one-off desktop licence costs less, as long as you have a Windows PC with Outlook.
How to repair a PST file online, step by step
The steps are nearly the same on every online service:
- Make a copy of the PST. Close Outlook, copy the file to a healthy local drive, and keep the original untouched.
- Check your connection. A multi-gigabyte PST can take a long time to upload, so use a stable connection and keep the browser tab open.
- Upload the copy. Open the tool in your browser and select the file. Stellar asks you to sign in; Recovery Toolbox asks for an email address.
- Check the preview. Before paying, make sure the folders you need (Inbox, Sent Items, Calendar, Contacts) appear with sensible item counts.
- Pay if needed and download. You receive a new PST. The service doesn’t change your original.
- Open the repaired PST in Outlook. Go to File > Open & Export > Open Outlook Data File and select it. If the damaged file is still attached to your profile, remove it under File > Account Settings > Account Settings > Data Files.
- Verify, then archive the old file. Spot-check old emails, attachments and calendar entries before you delete anything.
How to choose the right PST repair tool
Work through these in order and stop at the first one that fits:
- ScanPST hasn’t been tried yet? Run it on a copy first. It’s free and already on your PC.
- File is 500 MB or smaller? Use Stellar’s free tier.
- Mailbox holds confidential, client or regulated data? Use a desktop tool (PST Repair Kit, or the desktop editions of Stellar or Recovery Toolbox) so the file never leaves your computer.
- You only have an OST file, or no Windows PC? Use Recovery Toolbox Online.
- File is between 500 MB and 5 GB? Compare Stellar Premium ($29.99 flat) with Recovery Toolbox ($10 per GB). Under 3 GB, Recovery Toolbox is usually cheaper.
- File is larger than 5 GB? A desktop licence is almost always cheaper than paying per gigabyte.
Is it safe to upload a PST file?
A PST holds years of private email, attachments and contacts, so treat any upload as handing over a copy of your mailbox. Before you upload, read the service’s privacy policy and note how long it keeps files: 24 to 48 hours at Stellar, 30 days at Recovery Toolbox. Check also whether your employer’s data policy allows third-party processing.
If the retention period worries you, or your policy doesn’t allow it, skip online repair and use a desktop tool. You lose the convenience of a browser, but the data stays on your machine.
Final verdict
Start with ScanPST on a copy of the file. If that fails, Stellar Online PST Repair is the best first stop for most people, because it’s free up to 500 MB and lets you preview the result. For large PSTs, OST files, or repairs from a Mac or phone, Recovery Toolbox for Outlook Online is the most flexible, with no size limit and pay-per-GB pricing. If your mailbox is confidential or bigger than about 5 GB, PST Repair Kit fixes it on your own PC for a one-off $39.
Whichever you pick, always keep the original PST untouched until you’ve confirmed the repaired file has everything you need.
Frequently asked questions
Yes, if it’s 500 MB or smaller. Stellar Online PST Repair fixes one file of that size at no cost. Recovery Toolbox lets you preview the recovered folders and download a demo PST for free, but charges to download the full file.
No. Online services do the repair on their servers. You do need desktop Outlook to open the repaired PST afterwards, and desktop tools such as PST Repair Kit need Outlook installed to run.
Not always. Recovery depends on how much of the file is physically readable. Damage from bad sectors, ransomware or a truncated copy can mean some items are lost for good. That’s why previewing before you pay matters.
It can. ScanPST edits the original file and may discard items it can’t read. If it freezes mid-repair, the file can end up in a worse state. Always run it on a copy and keep the untouched original for a third-party tool.
Modern Unicode PSTs (Outlook 2003 and later) have a default limit of 50 GB. Older ANSI PSTs (Outlook 2002 and earlier) are limited to 2 GB, and files near those limits are far more likely to corrupt. Splitting or archiving large PSTs helps prevent repeat problems.
A PST is a standalone data file. An OST is a local cache of an Exchange or Microsoft 365 mailbox. If the account still works, Microsoft’s advice is to delete the OST and let Outlook rebuild it from the server. You only need a tool when the OST holds mail that no longer exists on the server; Recovery Toolbox and PST Repair Kit can convert it to a PST.
Yes, with an online tool, since Stellar and Recovery Toolbox both run in any modern browser. To use the result on a Mac, import the repaired PST into Outlook for Mac.
Sometimes. PST Repair Kit has a dedicated scan for deleted items, and other tools may surface them too. If the PST file itself was deleted, you need file-recovery software to get the file back before any of these tools can help.
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