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Corrupted OST or PST file: how to recover the emails

.pst and .ost files can get damaged by a shutdown in the middle of a write, a failing disk, cloud sync or oversized files. In most cases the content is still there; what gets lost are the indexes Outlook uses to find each item.

First: work on a copy

Close Outlook and copy the file to another folder before trying anything. Tools that repair in place, such as scanpst, change the original; if something goes wrong, the copy is your safety net.

How recovery mode works

1. Open the copy in the converter. If it doesn't open normally, use Try recovery mode; if it does, tick Recovery mode on the Convert screen.
2. The whole file is read and the indexes are rebuilt from the blocks and pages that are still intact, each one checked against its own checksum.
3. Folders and messages are copied into a new PST. Messages that lost their folder go to Recovered items, grouped by their original folder.
4. A damaged attachment is left out without dropping the message. The report shows how many items were saved and how many could not be read.

The original file is never changed, and the PST produced is a new, healthy file that Outlook opens normally.

What can and cannot be recovered

• Can: folders and messages whose data is still in the file, even when the indexes, folder tables or header are damaged.
• Sometimes: deleted messages that haven't been overwritten yet show up in Recovered items.
• Cannot: parts of the file that were overwritten or zeroed on disk. Whatever was there is gone, with any tool.

What about scanpst?

scanpst, which ships with Outlook, fixes the file itself and tends to discard whatever it can't fit back in. It doesn't open standalone .ost files. It's worth comparing: run OST Saver on one copy and scanpst on another, and keep the more complete result.