Exchange Server 2010 Mail Flow diagram

Email to the Hub Transport Server are submitted in 3 ways, they are

1. Through SMTP submission,
2. From the Pickup directory and
3. When a user inside the organization sends a message

Those emails submitted to the Hub transport server is picked up from the user’s Outbox by the store driver. The store driver is a software component of the Hub Transport server that delivers inbound messages to Exchange stores, the databases that contain public folder and mailbox stores
























Messages that are sent by users in your organization are picked up from the sender’s Outbox by the store driver and are put in the Submission queue on a server that runs the Hub Transport server role. When messages are submitted to the Hub Transport server, they’re processed by the categorizer.

Categoriser: The categorizer is a component of Exchange transport that processes all inbound messages and determines what to do with the messages based on information about the intended recipients.
In Exchange 2010, the Hub Transport server uses the categorizer to expand distribution lists and to identify alternative recipients and forwarding addresses. After the categorizer retrieves full information about the recipients, it uses that information to apply policies, route the messages, and perform content conversion.
If the email is sent to internal user, those emails are then delivered locally by the store driver to a recipient’s mailbox, if the emails is intended for external recipient they’re delivered remotely by using SMTP to send messages to another transport server.