We have Lemmy.world, Lemmy.ml, beehaw.org, I think even yiffit.net. If I log in using wefwef it asks me where I want to login. And when I make a new account using another instance, it says ”… Lemmy is federated, so you can interact with everything on lemmy.ml even if you’re registered on a different instance.“ So if I’m registered on lemmy.world, how can I interact with lemmy.ml?
But I can’t read any of their emails so it isn’t like email at all.
But if you both subscribe to the same mailing list you will both receive the same message.
I’m confident that “mailing lists” are not a thing most people will know about or understand today, and for a lot of people “email” and “gmail” are completely synonymous terms. A lot of people will have never interacted with an @yahoo account, I wasn’t aware they were even still in business.