Exchange 2013 hybrid upgrade to Exchange 2019 Hybrid, outlook keep prompting m365 login.

Question

Hi,

 

I have Exchange 2013 with Hybrid Modern Auth enabled. I am planning to migrate to Exchange 2019 hybrid. Outlook is 2019.

 

Everything works fine in EXCH13 hybrid environment. However when installed the first EXCH19 server in environment, internal users' outlook start to prompt m365 login box. No matter cancel or input credential, the box will prompt every 1 - 2 minutes. But once I switch off the EXCH19 server, everything works fine again without problems. External users might have this issue too, but haven't got any complain yet.

 

All mailboxes are still in EXCH13 now. No mailboxes on Cloud.

HCW should be fine as EXCH13 hybrid are running for long time already...

I have no idea what happening. No error logs, email flow seems ok. Please kindly assist!

Answer 1

Hi @LO CHI IN ，

Everything works fine in EXCH13 hybrid environment. However when installed the first EXCH19 server in environment, internal users' outlook start to prompt m365 login box. No matter cancel or input credential, the box will prompt every 1 - 2 minutes. But once I switch off the EXCH19 server, everything works fine again without problems. External users might have this issue too, but haven't got any complain yet.

Despite of the pop-up m365 login box, can the users use Outlook normally?
Could you remove all sensitive information like user name, domain, email address, etc and then share a screenshot of the prompt so that we can understand better about the situation?

Besides, if possible, please try catching a screenshot of the Connection status before and after shutting down the EXCH19 server and see if we can find any clues after comparing the output:

1. While Outlook is running, hold down the CTRL key and then right-click the Outlook icon in the system tray.
2. Select “Connection Status”. Catch a screenshot and make sure to obfuscate all personal information like domain name or email addresses."
   

In addition, based on my experience, when EXCH19 is switched on, you can try adding the registry key for an affected user, restart Outlook and see if there would be any difference:
(I**mportant: Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur.)

1. Exit Outlook, start Registry Editor (regedit.exe) .
2. In Registry Editor, locate and click the following registry subkey: HKEY_CURRENT_USER\Software\Microsoft\Exchange
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type AlwaysUseMSOAuthForAutoDiscover, and then press Enter.
5. Right-click AlwaysUseMSOAuthForAutoDiscover, and then click Modify, in the Value data box, type 1, and then click OK.
6. Exit Registry Editor.

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