If you’re a small shop, building a redundant Exchange infrastructure is time consuming and expensive. Even a simple Exchange setup with just a few users needs to be available all the time in order mail doesn’t get lost. You can hope that you server will never go down and plan the reboot (after the critical updates) to take place out of office hours.
Alternatively Server Room can act as a backup mailserver for your domain. If your primary mailserver goes down for any reason we will keep the messages in a queue waiting for the primary server to become available. If both servers are online or in some way connected to one another, the backup MX will typically queue a message briefly and immediately forward it to the primary MX. The backup MX acts as a store-and-forward mail server.