Symptoms
Outlook doesn’t use Modern Authentication to connect to Office 365. After you enter your credentials, they’re transmitted to Office 365 instead of to a token.
Cause
Outlook limits its choices of authentication schemes to schemes that are supported by RPC. But the authentication schemes don’t include Modern Authentication.
Resolution
Important
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.
- Delete OST
- Recreate Profile
- Try Below
Create the following registry key to force Outlook to use a newer authentication method for web services, such as EWS and Autodiscover. We recommend that users force Outlook to use Modern Authentication.
- Exit Outlook.
- Start Registry Editor
- In Registry Editor, locate and click the following registry subkey:ConsoleCopyHKEY_CURRENT_USER\Software\Microsoft\Exchange
- On the Edit menu, point to New, and then click DWORD Value.
- Type AlwaysUseMSOAuthForAutoDiscover, and then press Enter.
- Right-click AlwaysUseMSOAuthForAutoDiscover, and then click Modify.
- In the Value data box, type 1, and then click OK.
- Exit Registry Editor.