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
The book was dedicated in part to science fiction author Philip José Farmer, who had explored sexual themes in works such as The Lovers (1952).
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.