Update: The full timeline for retirement of Basic Authentication in Exchange Online is now published in Basic Authentication Deprecation in Exchange Online – September 2022 Update.
In February 2021...
Updated Sep 01, 2022
Version 19.0
Blog Post
Hello,
I have Exchange 2013 CU23 running in on-premises in a hybrid scenario with Exchange online, and AAD connect setup for Pass-through authentication (Autodiscover, MX records pointing to on-prem). All active users have been migrated to Exchange Online and using a mix of clients, but majority running Outlook 2016+. Due to auth being handled by our on-prem AD because of the pass-through config, will the conditional access policies I apply to users in Azure AD to block basic authentication work? if not, will configuring a New-authenticationpolicy and assigning to users work as described in this article:
https://docs.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/disable-basic-authentication-in-exchange-online
The above article does not provide much information for hybrid scenarios like my case.