Systems in a Mail Configuration
A mail configuration requires a minimum of two elements, which can be combined on the same system or can be provided by separate systems: a mail hub and mail clients. When you want users to be able to communicate with networks outside of your domain, you must also have a gateway. mailhost is a common DNS host alias assigned to the mail hub in any domain.
Figure 1 shows a typical electronic mail configuration that uses all elements. Each of these elements is identified and described in the following sections.
Figure 1. A Typical Electronic Mail Configuration
A gateway is a system that handles connections between ...