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Need Advice: Exchange Hybrid - password prompt when on-prem user open online mailbox user's calendar

Yang Yu 126 Reputation points
2021-08-04T04:51:21.947+00:00

We have moved pilot users' mailboxes to Exchange Online. During the test, we found that on-prem user keeps on getting password prompt when try to open online mailbox user's calendar. The credential pop-up wouldn't go away even typing in the right password few times. The only way to solves this is recreate the on-prem user's Outlook profile.

As we are doing the migration in batch, it will be annoying to rebuild the Outlook profile for quite large amount of users, who used to open other's calendar to check the availability in Outlook.

Is there any solution for this or workaround? Your advice will be highly appreciated.

Microsoft Exchange Hybrid Management
Microsoft Exchange Hybrid Management
Microsoft Exchange: Microsoft messaging and collaboration software.Hybrid Management: Organizing, handling, directing or controlling hybrid deployments.
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  1. grimson 21 Reputation points
    2022-03-09T15:34:54.517+00:00

    This helped me:
    https://learn.microsoft.com/en-us/outlook/troubleshoot/authentication/outlook-prompt-password-modern-authentication-enabled

    Outlook Client:

    Windows Registry Editor Version 5.00

    [HKEY_CURRENT_USER\SOFTWARE\Microsoft\Exchange]
    "AlwaysUseMSOAuthForAutoDiscover"=dword:00000001

    This should allow an on-premises Outlook Client/mailbox to access an Shared EOL mailbox.
    This will trigger a modern Authentication logon.

    I tried to open other mailbox folder like inbox but that access to a specific folder did not work. Guess you have to add the whole shared mailbox in your Outlook profile.
    It could be possible that this triggers the correct authentication and if you remove the full mailbox again this wil keep working and can access a folder instead of the whole mailbox.

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  2. KyleXu-MSFT 26,236 Reputation points
    2021-08-05T01:39:28.997+00:00

    @Yang Yu

    This phenomenon is caused by the change of Autodiscover. If you don't want to recreate Outlook profile, you could try to delete and add that user's calendar, check whether autodiscover record could updated successfully.

    If this phenomenon still exist, you may need to recreate profile after migration complete.

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