An SMTP-based message transfer agent (MTA) that runs under Unix. Developed at the University of California at Berkeley by Eric Allman in 1981, sendmail stores and forwards more mail than any other MTA on the Internet. In 1998, Allman commercialized the product by forming Sendmail, Inc. (www.sendmail.com), which offers a GUI interface for modifying the configuration file instead of dealing directly with more than a thousand lines of text. Sendmail, Inc. also offers a Windows NT/2000 version that includes the POP mail server and message store. Examples of mail clients developed for sendmail in the Unix world are elm, pine, mush and mailx. For information on the open source version, visit www.sendmail.org. See messaging system, BSD Unix and qmail.