Introduction to the Components of Mail Services

Many software and hardware components are required to establish a mail service. The following sections give a quick introduction to these components. These sections also provide some of the terms that are used to describe the components.

The first section, Overview of the Software Components, defines the terms that are used when discussing the software parts of the mail delivery system. The next section, Overview of the Hardware Components, focuses on the functions of the hardware systems in a mail configuration.

Overview of the Software Components

The following table introduces some of the software components of a mail system. Refer to Software Components for a complete description of all of the software components.

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

Overview of the Hardware Components

A mail configuration requires three elements, which you can combine on the same system or provide in separate systems.

A mail host – A system that is configured to handle email addresses that are difficult to resolve
A minimum of one mail server – A system that is configured to hold one or more mailboxes
Mail clients – Systems that access mail from a mail server

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

Figure 12-1 shows a typical electronic mail configuration, using the three basic mail elements plus a mail gateway.

Figure 12-1 Typical Electronic Mail Configuration

Diagram shows the dependencies between a mail gateway, a mail host, mail servers, mailboxes, clients.

Each element is described in detail in Hardware Components.