Our mail system will be based on a common design: one machine that acts as both a central mail server and the mail relay to the outside world. We'll use xenon for this task. All the remaining machines will act as mail clients and NFS-mount their mail directory (/var/mail) from the server. Figure 20.3 shows this configuration.
Figure 20.3. The mail system design.
The first thing we'll do is update our DNS entries so that xenon is recognized as the mail server for our domain. This will allow external machines to perform a DNS lookup and search for our MX records. We won't add any redundant servers or allocate any priorities ...