Many components are involved in the transport of messages through the Exchange Server 2010 mail flow pipeline. The Hub Transport server role diagram can help you understand the role each component plays in the processing of messages that enter the Exchange 2010 mail flow pipeline. Exchange administrators can use this information to help diagnose mail flow problems. The Hub Transport extensibility diagram can help you understand how the agents process a message that is in the Exchange 2010 mail flow pipeline. Developers can use this information to help create third-party agents and applications to work with Exchange 2010.