FreeOutlook 2013 to 365 OST files

Convert OST to PST.

Turn an Outlook OST file (the offline copy of a work, Microsoft 365 or Outlook.com mailbox) into a PST you can open in any Outlook, keep as an archive or use with every other tool here.

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OST

Drop the OST file here

or choose it. On Windows OST files are in %LOCALAPPDATA%\Microsoft\Outlook. Close Outlook first, or use a copy.

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    The result is checked before you can save it.
    Working
    Elapsed 0 s · your file stays on this computer
    How it works

    3 steps, nothing to install.

    1

    Find the OST

    On Windows it is in %LOCALAPPDATA%\Microsoft\Outlook, named after the mailbox. Close Outlook, or copy the file first.

    2

    Preview for free

    Every message is read and the new PST built and checked in memory, so you see the counts before anything is written.

    3

    Convert and save

    The PST is written, read back and every message compared with the OST. Open it with File › Open › Outlook Data File.

    Verified, not assumed

    Checked before you save it.

    The engine checks its own work. The result is read back from storage and compared with your original, and the report you can download lists every check.

    Every message of the OST is in the PST, compared one by one
    Folders kept as Outlook shows them
    Written in the standard PST layout that every Outlook opens
    The OST file is unchanged
    FAQ

    Questions, answered.

    What is an OST file?

    Outlook keeps an offline copy of a server mailbox (work Exchange, Microsoft 365, Outlook.com) in an .ost file. It only opens in the profile that created it; a PST opens anywhere.

    Can I convert an OST without the account or Outlook?

    Yes. The conversion reads the file itself, so the mailbox, the server and Outlook are not needed. OST files protected by Windows encryption cannot be read.

    Why is the PST bigger than the OST?

    Outlook 2013 and later compress the data in OST files; PST files are not compressed, so the same mail takes more space.

    What is not converted?

    Folder views and rules stored in the OST are left out (listed in the report). Attachments the OST never downloaded from the server cannot be recovered.

    Is my file uploaded?

    No. The engine runs inside your browser tab and reads the file from your disk. Results are written to your browser's private storage until you save them. Nothing is sent to a server.

    Related

    More PST tools.

    PST Viewer

    Open and read the PST without Outlook.

    ViewPST

    PST to MBOX

    For Thunderbird and Apple Mail.

    PSTMBOX

    Split PST

    By size, year, month or folder.

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