Outlook 2016 prompt for Modern Authentication & then stops working.

Question

Outlook 2016 prompt for Modern Authentication & then stops working.

Support_509 21

Hello, I've got an issue that I'm troubleshooting where new setups of Outlook 2016 work for a few minutes & then prompt for modern authentication. Once the prompt appears Outlook stops processing mail.

I've currently worked through both of the following links with no success.

https://learn.microsoft.com/en-US/outlook/troubleshoot/authentication/outlook-prompt-password-modern-authentication-enabled

https://answers.microsoft.com/en-us/outlook_com/forum/all/outlook-2016-modern-login-prompt-for-microsoft/06b7c339-89e6-428c-9922-55ae48b7cb81

We are configured with a single domain with an on-prem Exchange server. We do also have an O365 environment, but that is not configured yet & won't be for some time. Additionally, the Windows credential manager has been checked & nothing has been configured. What would be the next steps for resolving the issue?

Yuki Sun-MSFT 41,376 Reputation points Moderator

2022-12-07T06:16:56.873+00:00
Hi @Support_509 ,

From the 2nd link you shared above, seems like you have already tried adding the registry key "ExcludeExplicitO365Endpoint" with no luck, right? If this is the case, could you provide the following information so that we can understand better about the situation?

Does the issue only occur to a particular user? Or all users are affected?

When the prompt appears, can Outlook continue to work as usual if you enter the credential required? Or do you mean the prompt just keeps popping up?

What's the version of your Exchange server? Which CU build is it?

What's the detailed version of Outlook 2016? You can check it via File > Office Account > About Outlook.

Besides, it's suggested to run the "Test Email Autoconfiguration" when the issue occurs to see if any clues can be found:

a. While Outlook is running, click the CTRL key and then right-click the Outlook icon in the system tray, select “Test Email Autoconfiguration”.
b. Confirm that your email address is in the address field, uncheck “Use Guessmart” and “secure Guessmart authentication” boxes. Then click the “Test” button.
c. Once it runs, check the Log tab and Results tab.
Yuki Sun-MSFT 41,376 Reputation points Moderator

2022-12-09T08:48:05.257+00:00

Hi @Support_509 ,

Just checking in to follow up with this thread. Should you need more help on this, you can feel free to post back.

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Yuki Sun-MSFT 41,376 Reputation points Moderator

2022-12-07T06:16:56.873+00:00

Hi @Support_509 ,

From the 2nd link you shared above, seems like you have already tried adding the registry key "ExcludeExplicitO365Endpoint" with no luck, right? If this is the case, could you provide the following information so that we can understand better about the situation?

Does the issue only occur to a particular user? Or all users are affected?

When the prompt appears, can Outlook continue to work as usual if you enter the credential required? Or do you mean the prompt just keeps popping up?

What's the version of your Exchange server? Which CU build is it?

What's the detailed version of Outlook 2016? You can check it via File > Office Account > About Outlook.

Besides, it's suggested to run the "Test Email Autoconfiguration" when the issue occurs to see if any clues can be found:

a. While Outlook is running, click the CTRL key and then right-click the Outlook icon in the system tray, select “Test Email Autoconfiguration”.
b. Confirm that your email address is in the address field, uncheck “Use Guessmart” and “secure Guessmart authentication” boxes. Then click the “Test” button.
c. Once it runs, check the Log tab and Results tab.
Yuki Sun-MSFT 41,376 Reputation points Moderator

2022-12-09T08:48:05.257+00:00

Hi @Support_509 ,

Just checking in to follow up with this thread. Should you need more help on this, you can feel free to post back.

Answer 1

Andy David - MVP 157.8K MVP Volunteer Moderator

Try adding this registry entry to a workstation experiencing the issue:
https://gist.github.com/ridercz/dc485d38da104835559c1ed8b78afad0

https://medium.com/jj365/outlook-issue-with-direct-connect-to-office365-352dd29de65

Support_509 21 Reputation points

2022-12-09T12:24:34.553+00:00

Thanks 2AndyDavid! This worked perfectly, not sure these didn't work in the past, but thanks for the help!

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Outlook 2016 prompt for Modern Authentication & then stops working.

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