'Validate that the supplied email address is unique for the
site.'

def clean_email(self):

    if get_user_model().objects.filter(email__iexact=self.cleaned_data['email']):
        raise forms.ValidationError(_('This    email    address    is    already    in    use.    Please    supply    a    different    email    address.'))
    return self.cleaned_data['email']
