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search not working with old PST files

Alex W 60 Reputation points
2025-08-27T18:49:56.27+00:00

I need help with Outlook for Microsoft 365 on Windows 11. Search works perfectly for new emails in my main mailbox (OST), but it returns no results from my old PST files. Is there a registry key or a specific setting to force Outlook to correctly index these legacy PST files?

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  1. Chloe-L 1,585 Reputation points Microsoft External Staff Moderator
    2025-08-27T23:21:21.6233333+00:00

    Hi @Alex W,

    Welcome to Microsoft Q&A.

    Thank you for the detailed information. Based on your troubleshooting, this is likely an issue with how the Windows Search service is registering your PST files.

    Here is the most effective solution, which involves a registry change to force a re-index:

    Step 1: Modify the Registry

    1. Close Outlook and all other Office applications.
    2. Open the Registry Editor (regedit).
    3. Navigate to HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\Search.
    4. Right-click in the right pane and create a new DWORD (32-bit) Value.
    5. Name it ForcePSTIndexing and set its value to 1.

    Step 2: Check File Permissions

    Ensure your user account has full control permissions for the .PST files in their location on your computer.

    Restart Outlook after completing these steps. This should force the application to re-register the PST files, allowing the Windows Search service to index them correctly.

    Please let me know how these suggestions work for you, or if you'd like assistance in navigating Microsoft's support channels.

    Warm regards   

    Chloe L. | Microsoft Q&A Support Specialist

    ==============================================================

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  1. Mario Bressan 2,645 Reputation points Independent Advisor
    2025-08-27T19:55:33.9833333+00:00

    Hello, my name is Mario, and I would be happy to assist you with your issue.

    I’m sorry for what happened!

    Before I can provide you with instructions to try to resolve the issue, I need the following information:

    What is the size of the PST files? (this is very important)

    Which version of Microsoft Outlook were the files created in?

    Do you receive any error messages when accessing the PST files, or are they intact?

    I’ll be waiting for your reply so I can continue assisting you.

    Best regards,

    Mario B.

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