During the 1980s, I envisioned a (primitive) version of email that would come off telex machines. That is, a person would sit down at a keyboard, create a document, store it on a cartridge, stick the cartridge into say, a telex machine, send it to another terminal via modem, and the receiver could either print it out on his telex, or else download it to his screen, and read it off the screen. A similar result might have been obtained using fax machines. In either case, the "screen" would have represented a second delivery medium, as opposed to "just the fax" or "just the telex."
In actual fact, email became common in the mid-1990s when the Internet became commonly available. What is it about the internet that made it the driver of email? Put another way, why did it take so long for email to come into common use via the internet when it might have been made available through telex or fax machines perhaps 10-15 years earlier?