After you run the Enable-RemoteMailbox cmdlet, it fails, and errors show that ExchangeGuid is mandatory…
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.
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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:
- Enable modern authentication in Office 365 admin center
- 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.
Check the checkbox Turn on modern authentication for Outlook 2013 for Windows and later (recommended). Click on Save.
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.
Add the name AlwaysUseMSOAuthForAutoDiscover with the value data 1. Click OK.
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 »
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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