Error with email class in CI 3.1.8

im using valid_email like this

PHP Code:

$this->form_validation->set_rules('email', 'lang:valid_email', 'trim|valid_email|is_unique[USERS.EMAIL]|required'); 


Codeigniter use filter_var does not check if the domain existse. The email is valid. What is the error?
Does the email exist in the user table?