Keep in mind that the email began* as an application
of the ARPAnet file transfer protocol. Very soon
after the first nodes were hooked up in '69/'70,
people began using the file transfer capabilities
to leave notes for each other. It didn't take long
at all before someone said, "hey, lets put together
an addressing and delivery mechanism" and you had
email.
Something the military had been doing for some years, already...
--
Will