I don't like the email analogy, because people don't think about email like that, they are not really familiar with how email works. I like to summarize that differently: they only have to register on one instance and they can see every post in every other instances from that account, that's all. I read from people who thought they have to register on each instances separately, or they can login on a different instance with the same credentials. (Like you can login in the outlook app with your gmail and yahoo account, see the email analogy doesn't even true)

Don't recommend lemmy.ml to newcomers. Some instances already defederate from them, and they don't defederate lemmygrad and hexbear. Just pick any other general instance instead, lemmy.zip, sopuli, lemmy.ca etc is much better experience for new users.

This post also has some really good points for a general tips writeup like this: https://lemmy.zip/post/31641809