I personally think the email analogy does little to help.
What if federation is described as posts, comments and votes syncing between servers? This could make more sense to some people, and make it easier to explain some federation quirks (“this server stopped this other server from syncing with it”, “Votes differ slightly between instances because they are still syncing”)
What do you think?
I don’t see many people actually discussing the email analogy in the comments. This could indicate that people get the analogy, but you also stressed that “the same content is accessible from every server”, and gave links to a ton of instances, which I think is more useful for onboarding.