code: def validate_email(self, email):
          
          user, domain = email.rsplit("@", 1)
  
          return "@".join([user, domain.lower()])
docs: Validate the provided email address.
  
          Args:
              email:
                  The email address to validate.
  
          Returns:
              The provided email address, transformed to match the RFC
              spec. Namely, the domain portion of the email must be
              lowercase.