sendmail

Reliable, highly configurable mail transfer agent with utilities

Sendmail implements a general purpose internetwork mail routing facility under the UNIX operating system. It is not tied to any one transport protocol - its function may be likened to a crossbar switch, relaying messages from one domain into another. In the process, it can do a limited amount of message header editing to put the message into a format that is appropriate for the receiving domain. All of this is done under the control of a configuration file. Sendmail is a trademark of Sendmail, Inc.