Just for my general knowledge, when an instance bans a user, is that user just banned by the username they use? Or are they also banned by the email address they used as well? So if they tried to sign back up with the same email but a different username, they would get flagged/denied?

Also - when a community bans a user, is there like a “strike” system where like if they get banned from three communities, they get banned from the whole instance?