Except that usernames contain a domain name component, and the “bare” username likely isn’t globally unique, the UX is nearly the same as other microblogs. And as to that username bit, people are used to joe@gmail.com and joe@outlook.com being different people, and having to specify which one they’re trying to send an email to.

Everyone who’s both email and Twitter already understands all the basic concepts.

> And as to that username bit, people are used to joe@gmail.com and joe@outlook.com being different people, and having to specify which one they’re trying to send an email to.

User handles are unique in ATProto because of the domain, just like email. Not sure what the "except" part is about. Can you clarify? In ATProto, they are not "bare"

ActivityPub is the same, except they are tied to the server you join. In ATProto, they are decoupled from your data host so you can move your data and server without changing your handle. You can also change your handle without moving anything else, because handle points to a DID behind the scenes