public static boolean valida_mail(String email) {
        String mail_pat = "^[A-Za-z0-9_](\\.?[\\w-]+)*@[a-zA-Z]+(\\.[a-zA-z]+){1,2}$";

        if (email == null) {
            return false;
        }

        return email.matches(mail_pat) && email.length() <= 70;
    }