How to Transfer OST File to New Computer
In short: To transfer OST file to new computer, know that you usually should not copy the .ost at all, because it is tied to the Outlook profile that made it and will not open elsewhere. If the account still works, just add it on the new PC and Outlook rebuilds the OST from the server. If the OST is orphaned, convert it to a PST, move that PST across, then import it into classic Outlook. New Outlook cannot open local OST or PST files.
Why you cannot just move an OST file to a new computer
This one fact saves a lot of wasted effort. An OST is not a portable backup like a PST. It is a local cache of a mailbox that lives on a server, bound to the single Outlook profile, often the Windows account too, that created it. Move that file to another computer and Outlook there has no matching profile to attach it to, so it ignores the file. That is why the USB copy so many guides suggest almost never opens on the new PC. What you do instead depends on one question: is the original email account still working. If yes, you rebuild the cache. If no, the OST is orphaned and you convert it to a PST first.
Backup and Recovery Specialist, Corbett Software
“People spend an evening copying an .ost to a new PC and it just will not open, because the file belongs to the old profile. If the account still works, do not move the file at all, add the account and let Outlook rebuild it. Only an orphaned OST needs converting to PST.”
If the account still works: add it on the new PC
For a normal Exchange or Microsoft 365 account, there is nothing to carry over. The mail is on the server.
- On the new computer, install Outlook and go to File, then Add Account.
- Enter the same email address and sign in.
- Let Outlook sync. It builds a fresh OST from the server, with every folder and message back in place.
If you also want a portable copy to keep, export a PST from the old Outlook through File, then Open & Export, then Import/Export, then carry that PST over instead of the OST.
If the OST is orphaned: convert to PST and move it
An orphaned OST is one whose account is gone or whose server cannot be reached, so there is nothing to rebuild from. The file now holds the only copy of that mail, so it has to become a PST before any Outlook will open it.
The Corbett OST to PST Converter reads the OST directly, including orphaned and inaccessible files, keeps the folder structure and writes a PST that opens in any classic Outlook. A date and folder filter lets you convert only what you need, so a free demo edition lets you preview the mail first. It runs on every edition of Windows.
- On the old PC, install and open the tool, click Open, choose Email Data Files, then OST Files, then select your OST.
- Preview the mail to confirm it is the right file.
- Click Export, choose PST, apply any filter, then Save.
- Copy that PST to the new computer, then import it into classic Outlook through File, then Open & Export, then Import/Export.
Where your OST file lives
If you need to locate the OST to convert it, it sits in your local Outlook data folder.
- Open C:\Users\your-name\AppData\Local\Microsoft\Outlook, replacing your-name with your Windows user.
- Or in classic Outlook, go to File, then Account Settings, then Account Settings, then Data Files to see the exact path.
- Copy the OST somewhere safe before you convert it, so the original stays untouched.
Frequently asked questions
Can I just copy my OST file to a new computer?
Usually no. An OST is bound to the Outlook profile that made it, so a copied file will not open on another PC. Add the account so Outlook rebuilds it. For an orphaned OST, convert it to PST and move that.
How do I move Outlook to a new PC without losing mail?
For a live account, add it on the new PC and Outlook downloads everything again from the server. For safety, also export a PST from the old Outlook and keep it as a backup.
My OST account no longer exists. How do I move it?
That is an orphaned OST. Convert it to a PST with a converter, copy the PST to the new computer, then import it into classic Outlook. The PST holds all the mail the OST had.
Can New Outlook open a moved OST or PST?
No. New Outlook does not open local OST or PST files. Use classic Outlook to import a PST, then switch back if you prefer New Outlook for daily mail.
Where is the OST file located?
Under C:\Users\your-name\AppData\Local\Microsoft\Outlook. You can also check File, Account Settings, Account Settings, Data Files in classic Outlook for the exact path.
Is it safe to convert the OST to PST?
Yes. The conversion only reads the OST and writes a new PST, so the original file is never changed. You end up with both.