sendmail Features

The sendmail program provides the following features:

• It is reliable. It is designed to correctly deliver every message. No message should ever be completely lost.

• It uses existing software for delivery whenever possible.

• It can be configured to handle complex environments, including multiple connections to a single network type (like with UUCP or Ethernet). sendmail checks the contents of an address as well as its syntax to determine which mailer to use.

• It uses configuration files to control mail configuration instead of requiring that configuration information be compiled into the code.

• Users can maintain their own mailing lists. In addition, individuals can specify their own forwarding without modifying the domain-wide alias file (typically located in the domain-wide aliases maintained by NIS or NIS+).

• Each user can specify a custom mailer to process incoming mail, which can provide functions like returning an "I am on vacation" message. See the vacation(1) man page for more information.

• It batches addresses to a single host to reduce network traffic.

Figure 35-4 shows how sendmail interacts with the other programs in the mail system.

Figure 35-4 Interaction of sendmail With Other Mail Programs

The user interacts with a mail-generating and -sending program. When the mail is submitted, the mail-generating program calls sendmail, which routes the message to the correct mailers. Because some of the senders might be network servers and some of the mailers might be network clients, sendmail can be used as an Internet mail gateway.