Last Updated: October 26, 2017
After Modern Authentication is disabled, users may intermittently get prompted for their credentials in Outlook 2016 and have to repeatedly enter their username and password.
Note: Fiddler traces reveal 401/403 authentication failures to this endpoint: "https://outlook.office.com/api/v2.0/Me/InferenceClassification"
This scenario can occur if Focused Inbox and Modern Authentication for the tenant is turned on and then Modern Authentication is turned off. When this happens, Focused Inbox has already started working and keeps trying to connect resulting in these credential prompts.
Workaround #1: Turn Modern Authentication back on.
Workaround #2: If you want to keep Modern Authentication turned off, but avoid the credential prompting problem, do the following:
Turn Modern Authentication back on temporarily.
Turn Focused Inbox off and wait until all users who are using Focused Inbox get the "off" signal.
Turn Modern Authentication off.
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