public function countParts()
    {
        if ($this->_countParts) {
            return $this->_countParts;
        }

        $this->_countParts = count($this->_parts);
        if ($this->_countParts) {
            return $this->_countParts;
        }

        if ($this->_mail && $this->_mail->hasFetchPart) {
            // TODO: fetch part
            // return
        }

        $this->_cacheContent();

        $this->_countParts = count($this->_parts);
        return $this->_countParts;
    }