Is there a mod that will let me change the user add function so that when you sign up, the only thing you choose is your email address, not your user name and that will then automatically a) check your email address against a list such that only people with email addresses that are on the last can add themselves, and b) give the person a username looked up on the list based on their email?

If that can't be done, is there a mod that will allow users to only enter their email to sign up that will check their email against a list and only allow people with email addresses on that list to sign up?

If that can't be done, is there a mod that will allow me to mass-add users from a list of usernames and emails, instead of having to add them one by one?

Thanks!