Transport high availability seems to be one of those areas that Exchange Administrators do not really worry about—they just assume that an e-mail, once in Exchange, will always be delivered as long as the target mailbox is available. However, what if a server trying to send a newsletter to 40 recipients fails all of a sudden? What happens to those 40 e-mails? High availability for the Exchange transport pipeline is crucial to guarantee that no e-mails are lost while in transit. This is also very important in large deployments with dozens of servers, where e-mails sometimes cross countries before being delivered to their destination mailbox.

Before we delve into how Exchange 2013 further improves transport high availability, we first need to understand how the transport pipeline works in Exchange 2013. Please note that this is simply a high-level overview and not an in-depth explanation, as the main objective of this chapter is to understand how Exchange...