Microsoft Exchange Server 2013: Connectivity, Clients, and UM

The Front End Transport service

The Front End Transport (FET) service is discussed in much more depth in Chapter 2. However, it can be explained very simply. FET is a service that accepts SMTP connections and redirects them to Mailbox servers. It doesn’t queue mail for delivery, meaning that it doesn’t have to keep a queue database, participate in the Exchange 2013 shadow redundancy or Safety Net features, or do anything other than authenticate recipients (if configured to do so) and pass SMTP traffic to other servers. Because FET doesn’t queue anything, if it cannot immediately reach a proxy target, the FET service will return a transient SMTP error to the sender, forcing it to try again later. This is a neat trick because it shifts the burden ...