June 10, 2013

Exchange 2010 mail flow from start to finish

This refers to a typical Exchange 2010 organization, what fundamentally happens during MAPI mailflow.
A user sends email from Outlook (where their mailbox resides on the Mailbox server) and the message will be moved to the Outbox, mail will be picked up from the Store driver on the Hub transport server. The message is sent to the Submission queue. From the Submission Queue the message is sent to the Categorizer. The Categorizer will process all inbound messages and determines what to do with the message, it will apply policies, route message and perform content conversion.

1: Recipient resolution (resolves recipients email address to see if it is internal or external)
2: Routing (recipient is resolved and determines where message needs to be sent ie: external IP or next hop to Hub Transport server)
3: Content conversion (HTML, RTF, TXT)

The message is then sent to the Delivery queue. This is where the message is determined for either external delivery (these messages are then sent to the SMTP Send connector for external delivery). Or for internal email delivery, it will be passed to the correct Hub transport servers store driver, then delivered to the appropriate Mailbox server and Mailbox or Public folder.

In Summary:
1: Message is sent and waits in Outbox of outlook
2: Store driver on Hub Transport picks up this message from the oubox
3: Message is passed to the Submission Queue
4: Message is moved to the Categorizer where Recipient resolution, routing and content conversion takes place.
5: (For internal messages) email is then sent to the (destination ) Delivery queue of the hub transport server (eg: London HUB server)
(For external messages) email is then submitted to the Delivery Queue and then SMTP send to external destination.
6: Message is then moved to the Store Driver (at destination Hub Transport server) for delivery to the Mailbox server. Message is then delivered to mailbox or Public folder.

Below is Microsoft's diagram of how message flow works within 2010.

More high level Microsoft architecture for Hub transport can be seen here:


 ref: http://technet.microsoft.com/en-us/library/aa998825.aspx


  1. Its very helpful.I understood mail flow.

    Thank you

  2. Glad it helped.

  3. Nice, its very helpful to understand mail flow.

  4. It's Very helpful to understand Exchange Infra and became easy to troubleshoot.

  5. Great Work...Easy to understand...

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  7. can you please send me flowchart with explanation from send to receive