public function sendBatch(array $messages)
    {
        $body = '';
        /** @var Message\Message $message */
        foreach ($messages as $i => $message) {
            if (!$message instanceof Message\Message) {
                throw new InvalidArgumentException();
            }

            $body .= "[{$i}]\n";
            $body .= $message->toINI();
        }
        $body = trim($body);

        $request = $this->client->newRequest(
            'POST',
            $this->client->buildUriWithQuery('/SmSendPost.asp', ['encoding' => 'UTF8']),
            'text/plain',
            $body
        );

        $response = $this->client->sendRequest($request);

        return $this->parseMessageResponse($response);
    }