Setting up Basic Authentication in Exchange

1. Open the Exchange Admin Center.
2. Click on the “Servers”.
3. Select “all servers” in the servers list.
4. Choose “AutoDiscover” and click on the edit icon.
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5. Click on Authentication and check the “Basic Authentication”. Do not uncheck any other authentication methods.
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6. Likewise, Choose “EWS” and click on the edit icon.
7. Follow the step “5” to enable the “Basic Authentication” for EWS.

Sources:

Set-AuthenticationPolicy (ExchangePowerShell) | Microsoft Learn

Deprecation of Basic authentication in Exchange Online | Microsoft Learn