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, instea