Outlook continuously prompts for user credentials through basic authentication when Office 365 MFA is enforced

Question

If you only use Outlook to connect to Exchange Online then you don’t need to worry, as long as you are using Office 2019 or Office 2019 Pro Plus you’ll be fine come October 2020. Quote link

I am using Outlook version 2101 from Microsoft 365. I am not using custom API's, but I still see Outlook using basic authentication. For example, I pulled four log entries that occurred with using Outlook. Log details:

Application: Office 365 Exchange Online
Client App[1]: Offline Address Book
Client App[2]: MAPI Over HTTP
Client App[3]: Autodiscover
Client App[4]: Exchange Web Services

All 4 client applications fail to support modern authentication, which will fail when basic authentication ends. What do the users of Outlook at my company need to do to suspend using basic authentication? I have been attempting to enforce MFA but cannot get past Outlook continuously prompting users for their login credentials.

Answer 1

Solution: Check org setting for modern authentication. This must be turned on before MFA will work properly. You can also enable security defaults in the Azure portal, but this approach does not allow you to selectively enroll users into MFA.

Open Microsoft 365 admin center Show All Settings Org Settings Modern authentication Turn on modern authentication for Outlook 2013 for Windows and later

This setting allows for multiple exceptions, which will support your organization to continue to use basic authentication while you transition to modern authentication.

With this setting in place, you can selectively enforce Office 365 MFA on users. Each user will have to rebuild their locally installed Outlook profile before being able to use Outlook.