function sendInlineImages() {
  var message = GmailApp.getDraftMessages()[0];
  var bodyText = message.getBody();
  var rawContent = message.getRawContent();

  // Retrieve the multi-part boundary
  var multipartBoundary = rawContent.match(/multipart\/related; boundary=([\S]*)\s/i);

  // Skip for plain text or HTML emails without inline images
  if (multipartBoundary) {
    // Split the raw content on the multipart boundary to retrieve the inline content.
    var contentParts = rawContent.split('--' + multipartBoundary[1]);

    // Array of base64 encoded inline images
    var inlineImages = {};

    for (var i in contentParts) {
      var contentPart = contentParts[i].trim();

      // If this content part represents base64 encoded inline content?
      if (
        contentPart.match(/content-disposition: inline;/i) &&
        contentPart.match(/content-transfer-encoding: base64/i)
      ) {
        // Extract the mime-type and name.
        var contentType = contentPart.match(/content-type: ([^;]+);\s*name="([^"]+)"/i);
        var mimeType = contentType[1];
        var name = contentType[2];

        // Extract the content-id
        var contentID = contentPart.match(/content-id: <([^>]+)>/i)[1];

        // Split the content part into its header and base64 encoded data.
        // The header and base64 encoded part should be separated by a blank line.
        var subParts = contentPart.split(/^[^\S]+$/m);
        // Regex says split on lines that don't start with a non-space character

        // The 2nd part is the base64 encoded data.
        var base64enc = subParts[1].trim();

        // Create an image blob for the inline content.
        var blob = Utilities.newBlob(Utilities.base64Decode(base64enc), mimeType, contentID);

        inlineImages[contentID] = blob;

        // Replace the image source in the body text with the reference to the inline content.
        var regExp = new RegExp('src="[^"]+realattid=' + contentID + '[^"]+"', 'g');
        bodyText = bodyText.replace(regExp, 'src="cid:' + contentID + '"');
      }
    }
  }

  var subject = message.getSubject();
  var attachments = message.getAttachments();
  var bcc = message.getBcc();
  var cc = message.getCc();

  GmailApp.sendEmail('hello@labnol.org', 'Inline Image Test', 'labnol', {
    attachments: attachments,
    htmlBody: bodyText,
    cc: cc,
    bcc: bcc,
    inlineImages: inlineImages,
  });
}