Exchange 2016 + 2019 Mail Flow with Ports

Microsoft Docs provides detailed documentation on modern Exchange Server mail flow and the transport pipeline. That article helps you to

• Understand the Transport pipeline
• Understand the Transport service on Mailbox servers
• Understand the Transport service on Edge Transport servers

The detailed diagram showing the Exchange Server 2016 transport pipeline in the TechNet documentation does not show the TCP ports 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

• Front End Transport service
• Transport service
• Mailbox Transport service
• Mailbox Transport Delivery service

By default Exchange Server implements the following receive connectors

• Front End Transport service
  • Default Frontend SERVER, TCP 25
  • Outbound Proxy Frontend SERVER, TCP 717
  • Client Frontend SERVER, TCP 587
• Transport service
  • Default SERVER, TCP 2525
    Server SMTP connections connected to TCP 25 are proxied to this connector
  • Client Proxy SERVER, TCP 465
    Client submission connections connected to TCP 587 are proxied to this connector
• Mailbox Transport service
  • SERVER\Default Mailbox Delivery SERVER, TCP 475 (hidden)

Cross-server SMTP communication occurs on either TCP 2525 or TCP 475.

Link

• Mail flow and the transport pipeline 
• Receive Connectors

Enjoy Exchange Server!