code: def validate_email(self, email):
          
          user, domain = email.rsplit("@", 1)
          email = "@".join([user, domain.lower()])
  
          if self.instance and email and self.instance.email != email:
              raise serializers.ValidationError(
                  _(
                      "Existing emails may not be edited. Create a new one "
                      "instead."
                  )
              )
  
          return email
docs: Validate the provided email address.
  
          The email address is first modified to match the RFC spec.
          Namely, the domain portion of the email is lowercased.
  
          Returns:
              The validated email address.
  
          Raises:
              serializers.ValidationError:
                  If the serializer is bound and the provided email
                  doesn't match the existing address.