Why does an Outlook profile not work with a .ost datafile?

y zhang 60 Reputation points
2025-02-13T01:29:07.7033333+00:00

I tried to have set up two Outlook profiles on my windows 11 pc, one to open with a .pst datafile and another to open with a .ost datafile. But it gave warning message ".ost datafile is not a .pst datafile". What is the problem? Does an Outlook profile only work with a .pst datafile?

Outlook | Windows | Classic Outlook for Windows | For business
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Faery Fu-MSFT 19,896 Reputation points Moderator
2025-02-17T08:25:13.17+00:00

Hi @y zhang ,

If I create a new profile, may I link it to an existing Exchange email account (or a new email account)?

Yes, you can link a new Outlook profile to an existing Exchange email account or a new email account.

In order to avoid errors caused by OST file corruption, it is recommended that you move the old OST file and re-add the exchange account.

To recreate the OST file, first you need to locate the OST file. The default location of the OST file on your system is

C:\Users\user name\AppData\Local\Microsoft\user name\username.ost.

Right click on the OST file and select Delete.

Once you add the Exchange account, Outlook creates the new OST file.

For more detailed instructions, you can refer to the Introduction to Outlook Data Files (.pst and .ost)

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  1. Faery Fu-MSFT 19,896 Reputation points Moderator
    2025-02-13T09:00:29.9433333+00:00

    Hi @y zhang,

    The error message ".ost datafile is not a .pst datafile" indicates that Outlook is expecting a .pst file but is being provided with an .ost file instead.

    Here are some solutions that you can try:

    Separate Profiles:

    • Ensure that each Outlook profile is correctly configured to use the appropriate type of data file.
    • For a profile using a .pst file, make sure it is set up for a POP3 or IMAP account.
    • For a profile using an .ost file, ensure it is set up for an Exchange or Outlook.com account.

    Correct Configuration:

    • Open Outlook and go to File > Account Settings > Account Settings.
    • Under the Data Files tab, ensure that the correct data file (.pst or .ost) is associated with the corresponding account type.

    Creating a New Profile:

    • If the issue persists, you might need to create a new Outlook profile.
    • Go to Control Panel > Mail > Show Profiles > Add.
    • Follow the prompts to set up a new profile, ensuring you select the correct account type and data file.

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  2. Diane Poremsky MVP 17,526 Reputation points MVP Volunteer Moderator
    2025-02-13T01:55:00.0866667+00:00

    Ost files are created by IMAP and Exchange accounts and can only be opened by the account and profile that created it. You can make a copy of the ost and open it in another profile (like you can use PST files).

    Either add the account to Outlook and let it resync a new ost file or use a 3rd party utility to convert the ost file to a PST file.

    Diane Poremsky - M365 Apps & Services MVP
    https://www.slipstick.com

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