sendmail Features

The sendmail program provides the following features.

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

• sendmail uses existing software for delivery whenever possible.

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

• sendmail 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 mechanism without modifying the domain-wide alias file, typically located in the domain-wide aliases that are maintained by NIS or NIS+.

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

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

Figure 26-4 shows how sendmail interacts with the other programs in the mail system.

Figure 26-4 Interaction of sendmail With Other Mail Programs

As shown in Figure 26-4, the user interacts with a mail-generating and mail-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, you can use sendmail as an Internet mail gateway. See "Interactions of Mail Programs" for a more detailed description of the process.