A) All outbound HTTPS connections to Microsoft Online Services Reference: https://docs.microsoft.com/en-us/exchange/hybrid-deployment/prepare-for-hybrid-deployment To perform a hybrid deployment between an Exchange Online tenant and an on-premises Exchange Server organization, you must ensure that all outbound HTTPS connections to Microsoft Online Services are allowed. This is a prerequisite for installing the Microsoft Hybrid Agent.
D) Enable TLS 1.2. Reference: https://docs.microsoft.com/en-us/exchange/hybrid-deployment/prepare-for-hybrid-deployment To perform a hybrid deployment between an Exchange Online tenant and an on-premises Exchange Server organization, you must ensure that Transport Layer Security (TLS) 1.2 is enabled on your on-premises Exchange servers. This is a prerequisite for installing the Microsoft Hybrid Agent.