Microsoft Exchange
References
- https://practical365.com/configure-exchange-server-2019-smtp-anonymous-relay/
- https://practical365.com/exchange-2016-smtp-relay-connector/
- https://practical365.com/practical-exchange-understanding-smtp-relay-in-exchange-online/
- https://techcommunity.microsoft.com/t5/exchange-team-blog/updated-requirements-for-smtp-relay-through-exchange-online/ba-p/3851357#:~:text=Currently%2C%20to%20relay%20email%20through%20Exchange%20Online%2C%20two,matches%20your%20tenant%E2%80%99s%20Inbound%20Connector%20of%20OnPremises%20type.