About repairing PST files Outlook keeps a mailbox in a .pst file (or an .ost, its offline copy of an Exchange, Microsoft 365 or Outlook.com mailbox). When one is damaged - a crash or power cut while Outlook was writing, a file copied off a failing disk, a download cut short, a file past the old 2 GB limit - Outlook says the file “cannot be accessed”, “is not an Outlook data file” or has “errors”, and points to the Inbox Repair Tool, scanpst.exe. That only runs on Windows with Outlook installed, gives up on badly damaged files, and repairs the file in place. The repair programs sold as alternatives cost $29 to $99, and the “online” ones upload the whole mailbox to someone else’s server.
This page reads the damaged file without trusting it. The header is checked against its own checksum; the two indexes inside every PST (the B-trees that list the folders and messages, and where each piece of data sits) are walked page by page, and a page that fails its checks is skipped rather than followed. When anything is wrong - or always, with the deep scan - the whole file is read for pieces that still pass their own checks: each block of data carries its size, its id and a checksum, so blocks a broken index no longer reaches are found again, and so are old copies of index pages Outlook left behind, which is where deleted items come from. The folder tree is rebuilt from what survives: each folder and message names its parent, and a folder whose own record is gone is named from its parent’s list of subfolders. Items whose folder cannot be found go into a “Recovered items” folder rather than being dropped.
Everything recovered is written into a new Unicode PST by this site’s own PST writer (the one the OST to PST and EML to PST converters use), folders kept. Each email keeps its sender, recipients, dates, subject, plain, HTML or rich-text body, attachments, read or unread, internet headers and Message-ID; contacts, calendar items and tasks keep their other properties too, such as phone numbers, meeting times and categories. The damaged file is only read, never changed. It is read in place, a slice at a time, and in Chrome and Edge the new PST is written to disk as it goes, so a mailbox of several gigabytes can be repaired; other browsers build it in memory, which suits up to a gigabyte or so. It is free to use, with no account and no upload limit, and it runs entirely in your browser: nothing is uploaded, and while the page stays open, a feature you have already used keeps working offline.
What you can do Repair a PST or OST that Outlook or scanpst cannot open: Unicode PSTs (Outlook 2003 and later) and older ANSI ones (less tested, as few samples were at hand), OSTs including Outlook 2013 and later’s 4 KB-page format, files with the usual “compressible” encoding See in plain words what was damaged: the header, index pages, blocks failing their checksum, missing blocks, folders that lost their place Recover mail, contacts, calendar items and tasks with their attachments into a new PST, folder tree kept Find deleted items and messages the index lost with the deep scan, put in “Recovered items” Save everything as .eml files in a ZIP instead, for Thunderbird, Apple Mail or any other program See every item that could not be read, or only in part, by folder How to repair a PST file Close Outlook, then find the file: PSTs are usually in Documents\Outlook Files, OSTs in %LOCALAPPDATA%\Microsoft\Outlook (paste that into File Explorer’s address bar). Work on a copy if you can. Drop it onto the page. The report shows what is damaged, and how many items in which folders can be recovered. Press Save the repaired PST. In Chrome and Edge, choose where to save it first; it is written there as it goes. In Outlook, choose File, Open & Export, Open Outlook Data File, and pick the repaired PST. Drag what you need into your mailbox. Questions
Is this the same as scanpst.exe, the Inbox Repair Tool? It does the same job differently. Scanpst fixes the damaged file where it is, needs Outlook on Windows, and stops with “errors have been detected” on files it cannot handle. This page leaves the damaged file alone and copies what it can read into a new PST, works on any computer with a browser, and lists what it could not recover. It reads .ost files the same way as .pst files.
What does “Outlook data file cannot be accessed” mean? Outlook could not open the .pst or .ost it was told to use. Often the file is fine and only its place has changed - a moved file, a renamed folder, a disconnected drive, a file still in use by another program or set to read-only - and pointing Outlook at it again (File, Account Settings, Data Files) fixes it. If the file itself is damaged, scanpst or this page are the next step.
Can a damaged OST file be repaired as well as a PST? Yes. An OST is the same format as a PST, kept as Outlook’s offline copy of a server mailbox, so it is read and repaired the same way, and the result is a PST any Outlook can open. If the account still works, a damaged OST is normally just deleted and downloaded again from the server; repairing it matters when the account is closed, or mail was never synced back.
What can a PST repair not recover? Anything that is no longer in the file. A file cut short loses whatever was in the missing end; blocks overwritten by later data or zeroed by a failing disk are gone; a deleted item whose space Outlook has reused cannot come back. A message found by the deep scan with no index entry left keeps its own text and details but not its recipients and attachments, which were stored apart from it. Outlook’s rules, views and search folders are not copied, and files saved with the old “High encryption” setting cannot be read. The report says how many items were affected; no tool can honestly promise everything back.
Does it remove the password from a PST? The repaired copy has no password, but it does not crack one: a PST password is only a check Outlook makes before opening the file, not encryption of the mail, so the file can be read without it. Set a new password on the copy in Outlook if you want one.
Is it safe to repair a PST in the browser? The file never leaves your computer: it is read by code running in the page, and the repaired PST is made in the page too, then saved on your computer. The damaged file is never changed, so you can try scanpst, or this page again with the deep scan, afterwards. Message bodies are not displayed on the page at all. To just read a working PST or OST, or save its contacts as .vcf and its calendar as .ics, open it in the PST Viewer . To turn an OST into a PST without any damage involved, use OST to PST .