For an Exchange Admin it is important to have clear understanding of Messaging flow in Exchange and when it comes to prepare for an interview, having knowledge of Mail flow of Exchange Server 2003 is pretty important.
Exchange message flow is shown in the following figure.
Message flow in Exchange 2003 is as follows:
- An SMTP host connects to the SMTP transport engine on port 25, or an Outlook client places a message for sending in the database, or an inbound message is received from the MTA.
- Regardless of the origin, the message is transferred to the advanced queuing engine. If the message comes from a remote SMTP host, the SMTP protocol engine transfers the message to the advanced queuing engine, whereas if the message comes from a MAPI client, such as Outlook, or from MTA, the store driver transfers it to the advanced queuing engine.
- The advanced queuing engine then uses the categorizer to process received messages. The categorizer tries to resolve the originator, resolve recipients, and enforce message restrictions. Received messages are placed in one of two queues: a local queue with messages for recipients residing on the server, and an outbound pre-routing queue.
- From the local queue, the message transfers to the store driver, which is part of the Microsoft Exchange Information Store service, and is placed in the destination mailbox.
- To transfer messages from the pre-routing queue, the advanced queuing engine uses the routing engine to determine where the SMTP service should send the message. The routing module passes the message to the queue manager that finally places the message in a link queue to be sent through the SMTP service. The name of the link queue corresponds to the name of the destination domain. From the outbound queue, messages are sent to the next routing hop by the SMTP service.