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Electronic Mail.

15 Electronic Mail.

A few years ago, electronic mail (email) was a new thing that was mostly used by computer nerds. Today, if mail is broken on our machines, the secretaries are the first to complain; almost all departmental communication is done by electronic mail rather than by telephone, memos, or discussions.

15.1 Mail front ends.

15.2 The Mail Transport Agent

The transport agent is responsible for actually receiving and delivering messages. It should:

The predominant mail transport agent on Unix systems is sendmail.

15.2.1 The sendmail delivery agent.

The configuration file (/usr/lib/ is organized into three broad sections:

  1. Definitions of symbols, classes, options and parameters
  2. Address rewriting rules
  3. Definitions of mailers and delivery programs, and how to invoke them
sendmail allows the system administrator to define symbols, classes, options, priorities, and many other configuration parameters for mail delivery. The commands to do this usually precede the meat of the configuration file, the address rewriting rules. This is nice, since they are relatively easy to understand and give someone new to the config file a healthy dose of overconfidence.

15.2.2 The sendmail configuration file.

Configuration of sendmail is somewhat of a "Black Art." It is a very complex mail delivery agent that is designed to handle several mail transport mechanisms, address format translations, and delivery options. Each vendor will include enhancements for their own specific Unix implementations.

You can find the latest version of sendmail used by C&C at, There are also several example configuration files there. For documentation on configuration of sendmail, refer to "sendmail" by Bryan Costales, Eric Allman, and Neil Rickert.

If at all possible, use the Uniform Access hosts for email, or use an IMAP client (e.g., pine, PC pine, or MailStrom) from a Uniform Access IMAP server.

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