protected function _tls()
    {
        if ($this->_secure == 'tls') {
            $this->_send('STARTTLS');
            $this->_expect(220, 180);
            if (!stream_socket_enable_crypto($this->_connection, true, STREAM_CRYPTO_METHOD_TLS_CLIENT)) {
                throw new SMTPException(__('Unable to connect via TLS'));
            }
            $this->_ehlo();
        }
    }