In this chapter, we have explored all the improvements made by Exchange 2013 to transport high availability, namely shadow redundancy and Safety Net. Together, these two features guarantee that no e-mail is lost while in transit by keeping redundant copies of e-mails both before and after they are successfully delivered.

We also explored different methods used to load-balance both inbound and outbound mail flow at the same time, increasing high availability by preventing single points of failure.

Although shadow redundancy and Safety Net do a great job out of the box, business requirements will ultimately determine the configuration of these transport high availability features as well as the configuration of inbound and outbound mail flow.

In the next chapter, we will explore high availability for the Unified Messaging role.