This article states, that emails are 40 years old. Maybe that was the original case, for the US Military, the inventors of the Internet. Emails did not really become mainstream, until the early 1990s.
Dail-ups could take minutes or hours and an email could prematurely disappear into the cyber world.
NYC started to use emails, on a massive level, in the business & government communities, in the early 1990s.