This reg-edit essentially stops modern authentication in the Outlook client, which means you will not be able to use 2-factor auth. This is a Microsoft issue and they finally owned up to it by logging a service disruption message. Open the M365 Admin portal https://admin.microsoft.com; Go to Settings -> Org Settings -> Modern authentication .... "/>
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Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

Outlook not using modern authentication

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