examples: Added comments to SMTP multi example based on other MAIL examples

  if(!mcurl)

    return 2;

  /* This is the URL for your mailserver */

  curl_easy_setopt(curl, CURLOPT_URL, "smtp://mail.example.com");

  /* Note that this option isn't strictly required, omitting it will result in

   * libcurl sending the MAIL FROM command with empty sender data. All

   * autoresponses should have an empty reverse-path, and should be directed

   * to the address in the reverse-path which triggered them. Otherwise, they

   * could cause an endless loop. See RFC 5321 Section 4.5.5 for more details.

   */

  curl_easy_setopt(curl, CURLOPT_MAIL_FROM, FROM);

  /* Add two recipients, in this particular case they correspond to the

   * To: and Cc: addressees in the header, but they could be any kind of

   * recipient. */

  recipients = curl_slist_append(recipients, TO);

  recipients = curl_slist_append(recipients, CC);

  curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);

  curl_easy_setopt(curl, CURLOPT_URL, "smtp://smtp.example.com");

  /* We're using a callback function to specify the payload (the headers and

   * body of the message). You could just use the CURLOPT_READDATA option to

   * specify a FILE pointer to read from. */

  curl_easy_setopt(curl, CURLOPT_READFUNCTION, payload_source);

  curl_easy_setopt(curl, CURLOPT_READDATA, &upload_ctx);

  curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);

  curl_easy_setopt(curl, CURLOPT_MAIL_FROM, FROM);

  curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);

  /* Tell the multi stack about our easy handle */

  curl_multi_add_handle(mcurl, curl);

  /* Record the start time which we can use later */

  mp_start = tvnow();

  /* we start some action by calling perform right away */

  /* We start some action by calling perform right away */

  curl_multi_perform(mcurl, &still_running);

  while(still_running) {

    FD_ZERO(&fdwrite);

    FD_ZERO(&fdexcep);

    /* set a suitable timeout to play around with */

    /* Set a suitable timeout to play around with */

    timeout.tv_sec = 1;

    timeout.tv_usec = 0;

        timeout.tv_usec = (curl_timeo % 1000) * 1000;

    }

    /* get file descriptors from the transfers */

    /* Get file descriptors from the transfers */

    curl_multi_fdset(mcurl, &fdread, &fdwrite, &fdexcep, &maxfd);

    /* In a real-world program you OF COURSE check the return code of the

    }

  }

  /* Free the list of recipients */

  curl_slist_free_all(recipients);

  /* Always cleanup */

  curl_multi_remove_handle(mcurl, curl);

  curl_multi_cleanup(mcurl);

  curl_easy_cleanup(curl);

  return 0;

}