Turning off Basic authentication in the Microsoft 365 admin center does not turn off two legacy services.
- AllowBasicAuthOutlookService
- AllowBasicAuthReportingWebServices
These two settings can only be turned off via Exchange Online PowerShell.
Get-AuthenticationPolicy
Set-AuthenticationPolicy -Identity “policy name ” -AllowBasicAuthReportingWebServices:$false -AllowBasicAuthOutlookService:$false