SNDMSG was an early electronic mail program, chiefly notable because it was used to send what is considered the first networked email.
https://github.com/davepinch/pinchy.cc/blob/master/content/topics/computers/software/sndmsg/en.wikipedia.org.md
History of email (Wikipedia) The history of email entails an evolving set of technologies and standards that culminated in the email systems in use today.