Microsoft TechNet provides detailed documentation on Exchange Server 2016 mail flow and the transport pipeline. That article helps you to
The detailed diagram showing the Exchange Server 2016 transport pipeline in the TechNet documentation does not show the TCP ports being used by the Exchange Server 2016 components.
The following diagram is an updated version of the original diagram showing the TCP ports being used by
By default Exchange Server 2016 implements the following receive connectors
Cross server SMTP communication occurs on either TCP 2525 or TCP 475.
Enjoy Exchange Server!