When registering a new user the email field is not verified for existence.
If a user makes a typo when entering the email, the account will be created.
I understand it is left to developers if they will enforce email confirmation or not.
If we choose to enforce it, the user will not be able to confirm the email but the username will be used.
If he tries again to create the account, this time with the right email, he will not be able to use his intended username as it has been used by the wrong email.
How to handle this ?