PHPMailer\PHPMailer\SMTP::connect PHP Method

    public function connect($host, $port = null, $timeout = 30, $options = [])
    {
        static $streamok;
        //This is enabled by default since 5.0.0 but some providers disable it
        //Check this once and cache the result
        if (is_null($streamok)) {
            $streamok = function_exists('stream_socket_client');
        }
        // Clear errors to avoid confusion
        $this->setError('');
        // Make sure we are __not__ connected
        if ($this->connected()) {
            // Already connected, generate error
            $this->setError('Already connected to a server');
            return false;
        }
        if (empty($port)) {
            $port = self::DEFAULT_SMTP_PORT;
        }
        // Connect to the SMTP server
        $this->edebug("Connection: opening to {$host}:{$port}, timeout={$timeout}, options=" . var_export($options, true), self::DEBUG_CONNECTION);
        $errno = 0;
        $errstr = '';
        if ($streamok) {
            $socket_context = stream_context_create($options);
            //Suppress errors; connection failures are handled at a higher level
            $this->smtp_conn = @stream_socket_client($host . ":" . $port, $errno, $errstr, $timeout, STREAM_CLIENT_CONNECT, $socket_context);
        } else {
            //Fall back to fsockopen which should work in more places, but is missing some features
            $this->edebug("Connection: stream_socket_client not available, falling back to fsockopen", self::DEBUG_CONNECTION);
            $this->smtp_conn = fsockopen($host, $port, $errno, $errstr, $timeout);
        }
        // Verify we connected properly
        if (!is_resource($this->smtp_conn)) {
            $this->setError('Failed to connect to server', $errno, $errstr);
            $this->edebug('SMTP ERROR: ' . $this->error['error'] . ": {$errstr} ({$errno})", self::DEBUG_CLIENT);
            return false;
        }
        $this->edebug('Connection: opened', self::DEBUG_CONNECTION);
        // SMTP server can take longer to respond, give longer timeout for first read
        // Windows does not have support for this timeout function
        if (substr(PHP_OS, 0, 3) != 'WIN') {
            $max = ini_get('max_execution_time');
            // Don't bother if unlimited
            if (0 != $max and $timeout > $max) {
                @set_time_limit($timeout);
            }
            stream_set_timeout($this->smtp_conn, $timeout, 0);
        }
        // Get any announcement
        $announce = $this->get_lines();
        $this->edebug('SERVER -> CLIENT: ' . $announce, self::DEBUG_SERVER);
        return true;
    }