Part One

Together, message routing and transport are responsible for message delivery internally and externally. Message routing is the way that messages flow between servers within the organization and to other servers outside of the organization. Your routing topology, based on the routing groups and connectors that you define, dictates the path that these messages take to reach their final destination. Transport determines the way that messages are processed and delivered.

Simple Mail Transfer Protocol (SMTP) is the transport protocol that Microsoft® Exchange servers use to communicate with each other and to send messages using the routing topology. SMTP is part of the Microsoft Windows Server™ 2003 or Microsoft Windows® 2000 Server operating system. When you install Exchange on a server running Windows Server 2003 or Windows 2000 Server, Exchange extends SMTP to support additional SMTP commands for additional functionality. This functionality includes the ability to communicate the link state status (information about and costs of available messaging routes) and other Exchange functionality.

Part 1 contains the following topics:

• Understanding Routing Components

  Explains how routing groups, connectors, and link state information function to enable efficient message delivery.

• Understanding SMTP and Exchange Server 2003

  Provides a detailed overview of SMTP, including how SMTP works in Exchange Server 2003, and explains the process of sending and receiving Internet mail.

• Transport Dependencies for Exchange Server 2003

  Describes the components on which SMTP depends and discusses each component's interaction with SMTP.