Swift_Transport_AbstractSmtpTransport::_lookupHostname PHP Method

    private function _lookupHostname()
    {
        if (!empty($_SERVER['SERVER_NAME']) && $this->_isFqdn($_SERVER['SERVER_NAME'])) {
            $this->_domain = $_SERVER['SERVER_NAME'];
        } elseif (!empty($_SERVER['SERVER_ADDR'])) {
            // Set the address literal tag (See RFC 5321, section: 4.1.3)
            if (false === strpos($_SERVER['SERVER_ADDR'], ':')) {
                $prefix = '';
                // IPv4 addresses are not tagged.
            } else {
                $prefix = 'IPv6:';
                // Adding prefix in case of IPv6.
            }
            $this->_domain = sprintf('[%s%s]', $prefix, $_SERVER['SERVER_ADDR']);
        }
    }