Saturday, June 20, 2009

Message transport in Microsoft Exchange Server 2007

Message transport in Microsoft Exchange Server 2007 involves the interaction ofvarious components such as the Microsoft Exchange Mail Submission service, store driver, submission queue, and categorizer.

The Microsoft Exchange Mail Submission service is a notification service that runs on Mailbox server roles in Exchange Server 2007.

When a message becomes available for retrieval in the Outbox folder of a sender, the Microsoft Exchange Mail Submission service notifies a Hub Transport server in the local Active Directory site.

If there are multiple Hub Transport servers in the site, the Microsoft Exchange Mail Submission service evenly distributes notifications among all the available Hub Transport servers.

When the Microsoft Exchange Transport service starts on each Edge Transport server or Hub Transport server, the categorizer creates the local submission queue. The store driver on the Hub Transport server role retrieves the message, which is in MAPI format, from the sender’s Outbox folder and converts it to the Summary-Transport Neutral Encapsulation Format (S/TNEF). S/TNEF is a type of Transport-Neutral Encapsulation Format (TNEF), which has no plain text part and is in eight–bit binary format.

The store driver then submits the message to the submission queue and moves the message from the Outbox to the Sent Items folder. Messages can also enter the submission queue on a Hub Transport server from an SMTP Receive connector or from the Pickup directory.

The submission queue stores all messages on disk until the categorizer processes them. The categorizer processes the messages one at a time and always selects the oldest message in the submission queue first.

On an Edge Transport server, the categorizer verifies the recipient SMTP address of an inbound message and places it directly in the delivery queue. The message is then routed to a Hub Transport server.

On a Hub Transport server, the categorizer processes all inbound messages based on the information about the intended recipients. The categorizer makes copies of messages that have multiple recipients, determines routing paths, converts content format, and applies organizational message policies. After the categorizer processes the message, the message is removed from the submission queue.

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