email was Mac something something

Sorry, but you have the cart before the horse there. Hidden "header" implies RFC822 et al, but "email" not very broadly defined, doesn't require 'internet email' at all. It's not a semantic game. 822 type mail was simply "the winner" but the field was and still is large. Its valid to take the current most-popular, rfc822, and trace it's history back, but that won't show you all the things that went before, only those in that thread, and even that requires throwing out a lot of hard-to-categorize systems and techniques, and you can't call the resulting story "the story of email". It's common to do that sort of thing, but it's wrong. This is a general historiographic problem, but here there's thousands of other schemes. FidoNet started in 1984, probably the first amateur email system, but there were many, many other email systems that predated it by decades. Hell SAGE had multiple sites and modems, electronic transmission and storage of human-addressed email is a really obvious idea once you have a few givens. Western Union did automatic, electrical-plus-electronic unattended store-and-forward of telegrams (in a few high-traffic areas), that's pushing "e-mail" pretty hard!