The Exchange 2010 transport server role architecture diagrams are now available for download. The Hub Transport Role Architecture diagram can help you understand the different transport components involved in processing and routing messages, the different transport and routing agents that act upon messages and the SMTP events on which they are triggered, and visualize the mail flow.
The Hub Transport Extensibility diagram can help you understand how different transport agents process a message in the Exchange 2010 transport pipeline.
Both diagrams can be downloaded from Microsoft Exchange Server 2010 Transport Server Role Architecture Diagrams.
Note that Exchange 2010 includes internal or built-in transport agents which are not visible when you use the Get-TransportAgent or Get-TransportPipeline cmdlets. The list includes transport agents that implement Information Rights Management (IRM) functionality- the RMS Protocol Decryption agent, Journal Report Decryption agent, RMS Encryption agent, and Prelicensing agent, as well as the Journaling agent. To learn more about transport agents, see Understanding Transport Agents in Exchange 2010 documentation.