I have admin authorization for all new accounts turned on. If you register a user and then delete them, then re-register with the same email address that you just "deleted" you get an error message:

General Error
No values specified for SQL IN comparison

The registration works, the end user gets an email, the ACP shows the inactive user awaiting activation, the administrator DOES NOT get an email stating a new account has been created. Activating the account via the ACP or user management activates the user as it is supposed to.