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