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why is my standard version of outlook prompting for Office 365 credentials ????

dirkdigs 921 Reputation points
2021-11-30T17:26:18.73+00:00

hi we have a few users getting prompted for account credentials when using standard version of outlook . office ( VLSC version)

they are using on-prem exchange server (2019)
Office version standard 2019

we recently added their domain into an M365 tenant account and configured azure ad connect to sync some users to tenant but outook and exchange server still remain on-premise.

why would outlook be prompting for Azure account information in this scenario ?

scratching our heads.

Exchange | Exchange Server | Management

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  1. Manu Philip 20,206 Reputation points MVP Volunteer Moderator
    2021-11-30T18:59:37.637+00:00

    A password prompt can be seen in following situations

    A user’s mailbox is on-premises, and they have access to another user or shared mailbox which has already been moved to Exchange Online
    A remote archive has been created for the user
    Read more details and how to resolve this from here: outlook-prompt-password-modern-authentication-enabled

  2. Manu Philip 20,206 Reputation points MVP Volunteer Moderator
    2021-12-01T03:40:43.343+00:00

    It could be that, while you were performing the item 2, 'Exchange Hybrid Deployment' option was selected.
    153923-screenshot-2021-11-30-224626.jpg
    If that's the case, the process will written back certain 0365 attributes back to the on premises. So, even though you haven't migrated the mailboxes, there are some connections

  3. Manu Philip 20,206 Reputation points MVP Volunteer Moderator
    2021-12-01T04:03:20.877+00:00

    If your are not having any users in 365 at present, I don't see a requirement to select the option. But when you start adding any mailboxes in office 365, this is a must have option. The legacyExchangeDN of a moved mailbox is written back as an X500 address on-premises to the remote mailbox to avoid any mail delivery issues with cached addresses in outlook client.

  4. Kael Yao 37,746 Reputation points Moderator
    2021-12-01T07:37:48.737+00:00

    Hi @dirkdigs

    Have you added this value "ExcludeExplicitO365Endpoint" to the registry on the affected Outlook clients?
    If haven't yet, please try adding it and see if it can help with this issue.

    The path in registry is HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\AutoDiscover (if the Autodiscover key doesn't exist, you can manually create it)
    Please create a DWORD value named ExcludeExplicitO365Endpoint and set its value to 1.
    Then restart Outlook and see if it can connect successfully
    153936-71.png

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  5. Jasbir Saini 0 Reputation points
    2024-10-04T01:05:51.5766667+00:00

    @dirkdigs Were you able to find the root cause? We are experiencing the same issue after enabling Exchange Hybrid on-premises mailboxes using Outlook 2019 standard started prompting for credentials.

    All the mailboxes are on-premises with AD accounts synced to o365. We want to avoid creating the registry keys.

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