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Outlook prompts for password after migration to Office 365

You are migrating mailboxes to Office 365. After the mailbox migration finished, you start Microsoft Outlook. Outlook is stuck on the loading screen for minutes and then prompting for password. In this article, you will learn why Outlook prompts for password after mailbox migration to Office 365.

Outlook prompts for password after migration to Office 365

The mailboxes/mailbox databases are currently on Exchange 2010. After you finish completing the mailbox to Office 365, the user starts Outlook. It takes a very long time to connect. After waiting for minutes, a prompt shows up to enter credentials. Filling the credentials will not help you because it keeps asking for credentials.

Looking at the organization, we can see that three Exchange Servers are running:

  • 2x Exchange Server 2010
  • 1x Exchange Server 2016

The Exchange Server 2016 is going to be the Exchange Hybrid server. After the migration to Office 365 completes, the decommission of Exchange 2010 servers will start. The only Exchange Server that is going to stay on-premises is the Exchange Server 2016.

Why did Outlook not accept the credentials, and what is the solution for Outlook prompts for password after migration to Office 365?

Solution for 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.
From August 1, 2017, modern authentication is enabled by default for Exchange Online and Skype for Business, and SharePoint Online.

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

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

Enable modern authentication in Microsoft 365 admin center

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.

Outlook prompts for password after migration to Office 365 modern authentication

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

Outlook prompts for password after migration to Office 365 enable modern authentication

After enabling modern authentication, follow the next step. Was modern authentication already enabled? That’s great and proceed further.

Add registry key AlwaysUseMSOAuthForAutoDiscover

I recommend to add the registry key for the user only and start Outlook. If that works, roll it out with a Group Policy Object (GPO).

Exit Outlook and start Registry Editor on the system that is having the problem. Go to the path HKEY_CURRENT_USER\Software\Microsoft\Exchange. Add a new DWORD (32-bit) Value.

Outlook prompts for password after migration to Office 365 add DWORD

Add the name AlwaysUseMSOAuthForAutoDiscover with the value data 1. Click OK.

Outlook prompts for password after migration to Office 365 add DWORD value

After the change is applied, start Outlook. Outlook client is not prompting for password anymore, and it connects immediately. Did this work for you?

Keep on reading: Complete migration batch with PowerShell »

Conclusion

In this article, you learned why Outlook prompts for password after migration to Office 365. The solution to this problem is to enable modern authentication in Microsoft 365 admin center. After that, configure a registry key on the systems that are using Outlook. The registry key will force Outlook to make use of Modern Authentication.

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ALI TAJRAN

ALI TAJRAN

ALI TAJRAN is a passionate IT Architect, IT Consultant, and Microsoft Certified Trainer. He started Information Technology at a very young age, and his goal is to teach and inspire others. Read more »

This Post Has 3 Comments

  1. Ali thank you for taking the time to post this. We had this problem, and have a open case with MS to resolve it. I found your article, and tested it out and it looks like it did the trick. You don’t know how much I appreciate it.

    Our symptoms were slightly different. We started to get Outlook authentication prompts after the first mailbox was moved to EXO, and everyone else was still on prem.

    Thanks again.

    1. We are having this exact same issue. We migrated two test mailboxes to EXO and as soon as they “completed” the migration we started getting reports that our on-prem users were getting pop-ups to enter their credentials. We don’t use MAPI over HTTPS as our Outlook 2016 still use RPC over HTTPS. Adding that registry key did not resolve our issue. Anyone have any ideas?

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