I imagine if you tried “releasing” IMAP and SMTP email (with whatever cleanups and encryption you wanted to choose) now as a new open standard, in a world where email never existed, there is no chance it would take off.
My theory is that email took off because of how well it used already existing concepts from paper mail. People picked up the concepts behind paper mail as children. New concepts are hard and I think we tend to overlook that fact.
