Shadow Rebundancy and SMTP delay Acknowledgement

           
         Exchange 2010 introduced the shadow redundancy feature to minimize the loss of any message during delivery after it enters the Exchange organization. Exchange Transport servers achieve this by using the shadow redundancy SMTP protocol extension.

        However, in any organization Exchange Transport servers need to communicate with other third-party SMTP servers that may not support the shadow redundancy protocol. Transport servers delay sending acknowledgement to incoming messages until they verify final delivery within the organization. However, when a specific threshold was reached, the Transport server issued an acknowledgement even if final delivery wasn’t verified. This presented a scenario where messages received from hosts that don’t support shadow redundancy can be lost in transit.

        To address this issue, a new feature called shadow redundancy promotion is introduced in Exchange 2010 SP1. When faced with the scenario described above, instead of issuing an acknowledgment without delivery confirmation, a Transport server now routes the message to any other Transport server within the site so that the message is protected by shadow redundancy.

      Suppose  that all messages are typically delivered within 25 seconds in your environment, but due to performance requirements, you don’t want to delay acknowledgement more than 20 seconds for messages received from the Internet. After analyzing the message flow, you conclude that 95 percent of messages are delivered within the 20 second interval. This example configures the Receive connector from the Internet to delay acknowledgement for only 20 seconds. In this scenario, your environment provides shadow redundancy for 95 percent of messages received from the Internet.

Set-ReceiveConnector "From the Internet" -MaxAcknowledgementDelay 00:00:15.

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