locked
Client mail submission, Transport Services, Mail Flow and redundancy RRS feed

  • Question

  • Hello,

    I've read my way through the Exchange documentation, eg. Mail flow and the transport pipeline, but could not clearly understand, how mail flow and redundancy (shadow redundancy and safety net) will affect an e-mail send from the Outlook client (MAPI over HTTPS) on my computer - either to an internal colleague or an external user.

    Questions still open:

    1. In which cases will the Mailbox Transport Submission service on one Exchange server use "it's own" SMTP to send an e-mail and when will the Transport services SMTP be used? Questioned because both services can connect to Mailbox Transport Delivery service 's SMTP Receive on other Exchange servers in my organization.

    2. In which case will the e-mail from my Outlook client end up in shadow redundacy or safety net queues? Questioned because I've understood, that only mails flowing through Transport service will be put in these queues - hence see question 1.

    Kind regards!


    • Edited by COWegner Friday, April 20, 2018 10:44 AM technet link
    Friday, April 20, 2018 10:43 AM

All replies

  • Hi COWegner,

    For your first question, when we send or receive mails to or from an external domain, mails will through the Transport service. If we send mail internally, it will only though Mailbox Transport Service between mailbox server role.

    About your second question, if Shadow redundancy is enabled, when a message arrives on a Mailbox server in the transport high availability boundary, Exchange tries to maintain two redundant copies of the message on Mailbox servers within the boundary. Safety Net is a queue that's associated with the Transport service on a Mailbox server, this queue stores copies of messages that were successfully processed by the server.

    Regards,

    Kyle Xu


    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.

    Click here to learn more. Visit the dedicated forum to share, explore and talk to experts about Microsoft Teams.

    Monday, April 23, 2018 10:08 AM
  • Hello Kyle,

    thank you for the explanation. Maybe you could elaborate question 2 a little bit regarding my internal Outlook client scenario. Let me explain, why I still have this question:

    For an external SMTP connection, Shadow redundancy and Safety Net will behave as you said. From what I understand, both work only in the Transport Service, but not in the Mailbox Transport Service. From that comprehension a message, that is only going through Mailbox Transport Service, hence an internal message, will never get the benefit of Show Redundancy or Safety Net, right?

    OK, back to my example: Outlook, using MAPI over HTTP, will not connect to the Transport Service's nor the Mailbox Transport Service's SMTP endpoint - am I right? And...maybe the recipient's mailbox isn't on the same server, that the Outlook client is connected to (CAS).

    So what's the flow of an internal Outlook message, which Exchange Transport Services will be touched and is there any redundancy or safety for the message on it's way to the recipient?

    Kind regards,

    Carsten Wegner



    • Edited by COWegner Monday, April 23, 2018 3:02 PM
    Monday, April 23, 2018 10:49 AM
  • Hi,

    Shadow redundancy is enabled by default.

    Shadow is done only by the Transport Service.
    Every message is redundantly persisted (shadowed) before its receipt is acknowledged to the sender.
    If shadow can't be made, Transport Service will reject sender.

    ---------------------------

    Please click on "Mark as Answer" and “Vote as Helpful” on the post that helps you, this can be beneficial to other community members.

    Monday, April 23, 2018 11:54 AM
  • Thanx also, Faisal.

    But please consider my specific question, which can't be answered by your reply. For it's still unclear whether an internal message, sent by an Outlook client (e.g. Outlook 2016), will ever reach the Transport Service. 


    • Edited by COWegner Monday, April 23, 2018 12:44 PM
    Monday, April 23, 2018 12:40 PM
  • Hi,

    The Transport Service Performs all routing decisions for internal and external messages. SMTP messages received from inside the organization enter the transport pipeline via the Transport service present on a Mailbox server.

    Monday, April 23, 2018 3:07 PM
  • Hi,

    The Transport Service Performs all routing decisions for internal and external messages. SMTP messages received from inside the organization enter the transport pipeline via the Transport service present on a Mailbox server.

    Faisal,

    what you say is kind of contrary to what Kyle stated above: "If we send mail internally, it will only though Mailbox Transport Service between mailbox server role."

    Also I am not sure wether the Tarnsport Service does the routing decision or Transport Service and Mailbox Transport Service just utilize the same routing information. See also here.

    Either way, I don't see any clearer for Outlook will not do SMTP.

    Monday, April 23, 2018 4:41 PM