To simplify the setup instructions, the following sections tell you how to set up individual mail hubs, mail clients, and gateway hosts. If a system in your mail services configuration is acting in more than one capacity, simply follow the appropriate instructions for each type of system. For example, if your mail hub and gateway are the same system, follow the directions for setting up that system as a mail hub and then follow the directions for setting up the same system as a mail gateway.
The following procedures for setting up a mail server and a mail client apply when mailboxes are NFS-mounted. You do not need to follow these procedures when mailboxes are maintained in locally mounted /var/mail directories