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Outlook Desktop not syncing with OS app

Makani 0 Reputation points
2025-10-22T21:00:43.4066667+00:00

I use Outlook on Window laptop and Apple phone. The account is set up as IMAP.

Received emails and sent emails are synced fine. What is not syncing is if I already read the emails or not.

And If I replied to the email from phone, it will not have the reply icon on Desktop version. In some instances, when I reply form Desktop, Desktop still will not show the reply icon. On the phone, whatever I reply from the phone will have the sent icon.

If I read the emails on Desktop, it will not reflect on phone. If I read on phone, it will reflect on Desktop.

Does anyone know how to fix these problem?

Outlook | Outlook for mobile | Outlook for iOS | For home
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  1. Kimberly Olaño 16,260 Reputation points Independent Advisor
    2025-10-22T22:34:35.06+00:00

    Hello! Makani. Thanks for explaining that clearly. That helps narrow down the issue.

    It seems you're using the New Outlook on Windows. The new version uses a different sync model that sometimes loses IMAP state updates. Switch back to the classic Outlook.

    1. Turn off the “New Outlook” toggle at the top right.
    2. Reopen classic Outlook.
    3. Let it resync.

    See if this helps. If you need further assistance, just let me know.

    Best regards,

    Kimberly

  2. Kimberly Olaño 16,260 Reputation points Independent Advisor
    2025-10-23T22:56:42.3966667+00:00

    Actually, you have to toggle it off to use the classic outlook. How is the syncing when using classic outlook?

  3. Kimberly Olaño 16,260 Reputation points Independent Advisor
    2025-10-24T00:14:45.5566667+00:00

    I see, thanks for confirming. Now we have to verify Outlook IMAP root folder path.

    Sometimes the IMAP root folder path isn’t set correctly, and that breaks flag syncing.

    1. In Outlook → File > Account Settings > Account Settings.
    2. Double-click your IMAP account.
    3. Click More Settings > Advanced tab.
    4. Check the Root folder path field:

    For Gmail → enter "[Gmail]" (without quotes)

    For most others (Yahoo, Outlook.com, Zoho, etc.) → leave it blank

    1. Click OK, restart Outlook.
  4. Kimberly Olaño 16,260 Reputation points Independent Advisor
    2025-10-25T03:26:23.4766667+00:00

    Yes, that’s actually a very plausible cause.

    When you try the New Outlook for Windows and then switch back to Classic Outlook, it can leave behind partially migrated settings or cached account data that interferes with normal IMAP syncing, especially for flags like “read/unread” and “replied.”

    Speaking about leftovers from the New Outlook switch, do this in Classic Outlook:

    Remove and re-add the IMAP account completely

    Go to File → Account Settings → Account Settings.

    Select your IMAP account → click Remove.

    • Don’t worry — emails are still on the server since it’s IMAP.

    Close Outlook.

    Navigate to:

    C:\Users\<YourUser>\AppData\Local\Microsoft\Outlook\

    and delete or rename any .ost or .pst file tied to that account.

    Reopen Outlook.

    Add the same IMAP account fresh.

  5. Kimberly Olaño 16,260 Reputation points Independent Advisor
    2025-10-25T23:35:57.8333333+00:00

    You will not lose emails, but you might lose locally stored contacts or calendar entries if they are not synced to the server.

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