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Find Outlook's .ost file

With an Exchange or Microsoft 365 account, Outlook for Windows keeps a local copy of the mailbox in an .ost file. It sits in the Windows profile folder.

Step by step

  1. From Outlook

    File, Account Settings, Account Settings, Data Files tab: select the account, then "Open File Location".

  2. Or from File Explorer

    Type %LOCALAPPDATA%\Microsoft\Outlook in File Explorer's address bar: the file is usually named after the address, such as "first.last@company.com.ost".

  3. Close Outlook

    While Outlook is open the file is locked: close Outlook before copying it.

  4. Copy

    Copy the .ost elsewhere (another folder, a drive) and work on the copy.

Good to know

  • The .ost is only a copy: it often holds just a recent period of the mailbox (the mail-to-keep-offline setting), and messages not yet synchronised are not in it.
  • The AppData folder is hidden by default; the address bar still gets you there.
  • The new Outlook for Windows does not create an .ost file.
  • For the complete mailbox, a PST export made by Outlook or by the administrator is safer: see the PST guide.

Then, in Klarinbox

Drop the copy of the .ost on Open a PST file: it is read like a PST, folders, search and filters included, without Outlook and without the account.

Frequently asked questions

Can an .ost be opened without the account that created it?
Klarinbox reads it directly, without the account or Outlook. Outlook itself refuses to open another profile's .ost.