Advanced Queuing Engine - SMTP Architecture
The advanced queuing engine is a key component in Exchange 2003 message handling, because all messages must pass through this engine, even when sender and recipient are located on the same server running Exchange Server 2003. This enables Exchange Server 2003 transport components to process every message. No e-mail message can bypass the transport subsystem.
Advanced Queuing Engine - Events
Please find this article, which illustrates, the advanced queuing engine "how it" acts as an information controller or dispatcher of system, store, and transport events to process each message after it reaches the SMTP transport subsystem.
The above engine dispatches the following events: