System Administration Guide, Volume 3

Introduction to Mail Services Terminology

Many software and hardware components are required to establish a mail service. The following sections give a quick introduction to these components and some of the terminology used to describe them.

The first section defines the terminology used when discussing the software parts of the mail delivery system. The next section focuses on the functions of the hardware systems in a mail configuration.

Mail Services Software Components Overview

The following table introduces some of the software components of a mail system. See "Mail Services Software Terminology" for a complete description of all of the software components.

Component	Description
.forward files	Files that can be set up in a user's home directory to redirect mail or send mail to a program automatically
mailbox	A file on a mail server that is the final destination for email messages
mail addresses	Contains the name of the recipient and the system to which a mail message is delivered
mail aliases	An alternate name used in a mail address
mail queue	A collection of mail messages that needs to be processed by the mail server
postmaster	A special mail alias used to report problems and ask questions about the mail service
sendmail configuration file	A file that contains all the information necessary for mail routing

Hardware Components of a Mail Configuration

A mail configuration requires three elements, which can be combined on the same system or provided by separate systems:

A mail host - A system configured to handle email addresses that are difficult to resolve
At least one mail server - A system configured to hold one or more mailboxes
Mail clients - Systems that access mail from a mail server

When you want users to communicate with networks outside your domain, you must also add a fourth element, a mail gateway.

Figure 33-1 shows a typical electronic mail configuration, using the three basic mail elements plus a mail gateway.

Figure 33-1 Typical Electronic Mail Configuration

Each element is described in detail in "Hardware Components of a Mail Configuration".