public function isRole($email)
    {
        if (! $this->isEmail($email)) {
            return null;
        }

        $user = $this->userFromEmail($email);

        if ($user) {
            // Load disposable domains
            if (is_null($this->role)) {
                $this->role = include('data/role.php');
            }

            // Search array for hostname
            if (in_array($user, $this->role)) {
                return true;
            }

            return false;
        }

        return null;
    }