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

dirkdigs 921 Reputation points

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 Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Manu Philip 16,911 Reputation points MVP

    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 16,911 Reputation points MVP

    It could be that, while you were performing the item 2, 'Exchange Hybrid Deployment' option was selected.
    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 16,911 Reputation points MVP

    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-MSFT 36,836 Reputation points Microsoft Vendor

    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

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