Some users getting strange authentication windows post-migration to 365.

Question

We're in the process of migrating users from Exchange 2016 on-premise to 365. I have some migrated users reporting some strange issues after they've been migrated.

• The first issue is some users are seeing what starts to be (presumably) a Microsoft Account authentication box, but then it goes away. It may be up for a microsecond, or it may be up for 2-3 seconds. It doesn't seem to occur at regular intervals, and I've never seen it myself. A user finally was able to hit Print Screen in time to capture it, though.

• In addition, many users are being prompted for credentials post-migration. This may happen 3-4 times per day. The authentication box is a Windows authentication box however, not a Microsoft Account authentication box. Their password is not accepted when entered.

Sometimes it even shows Windows Mail instead of Microsoft Outlook.

Are these issues related? All machines are Windows 10 machines joined to our local domain.

Answer 1

Hi @Joe Grover

Please refer to the solution peovided in this article: Outlook prompts for password after migration to Office 365

A couple of scenarios of how this can happen:

• Microsoft Outlook connects to your primary mailbox in an on-premises Exchange server by using RPC, and it also connects to another mailbox located in Office 365.
• You migrate your mailbox to Office 365 from an Exchange server that Outlook connects to by using RPC.

Outlook doesn’t use modern authentication to connect to Office 365. The solution is to:

• Enable modern authentication in Office 365 admin center
• Add a registry key on the computers to force Outlook to use the newer authentication method

Log into Microsoft 365 admin center. In the left-hand navigation, click on Settings and follow with Org settings. At the top, click on Services, scroll down, and click on Modern authentication.

Check the checkbox Turn on modern authentication for Outlook 2013 for Windows and later (recommended). Click on Save.

HKEY_CURRENT_USER\Software\Microsoft\Exchange Add a new DWORD (32-bit) Value.
Add the name AlwaysUseMSOAuthForAutoDiscover with the value data 1. Click OK.

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