1. This looks like a normal use case. It depends on your business, if you end up collecting more than just an email (e.g. SSN, phone #, etc.), then you can add

1. This looks like a normal use case. It depends on your business, if you end up collecting more than just an email (e.g. SSN, phone #, etc.), then you can add a logic to prevent the creation of a new account from the same user. Otherwise, it looks just like the creation of a new account and shouldn't be handled has an exception by your app. 2. On the user side you only present an email as a login. Though, on the implementation side you still need a user_id as your primary key. You can update the email attribute at anytime for an existing user_id. That involves an extra step to setup some sort of security questions so that a user can update the email address without having to access the account.