This download contains architectural diagrams that illustrate the Microsoft Exchange Server 2010 Hub Transport server role and Hub Transport extensibility.
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. (From Microsoft Site)
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