function extractData(data, startStr, endStr) {
  // This function extracts text between two strings
  // i.e. extractData("Good_news,_everyone!", "Good_", ",_Everyone!") will return "News"
  var startIndex, endIndex, text = 'N/A';
  
  startIndex = data.indexOf(startStr);
  
  if(startIndex != -1) {
    startIndex += startStr.length;
    text = data.substring(startIndex);
    
    if(endStr) {
      endIndex = text.indexOf(endStr);
      
      if(endIndex != -1) {
        text = text.substring(0, endIndex);
      } else {
        text = 'N/A';
      }
    }
  }
  return text;
}

function parseEmailMessages() {
  // var threads = GmailApp.search();
  // Have to get data separate to avoid google app script limit!
  var start = 0;
  var sheetId, sheet, threads, labelName, label;
  // SheetId is your google spreadsheet id
   
  labelName = 'Parsed';
  sheetId = 'abc1234567';
  label = GmailApp.getUserLabelByName(labelName)||GmailApp.createLabel(labelName);
  sheet = SpreadsheetApp.openById(sheetId).getSheets()[0];
  threads = GmailApp.search('in:inbox -label:'+labelName, start, 100);
  // Search query for messages without specific label
  
  for (var i = 0; i < threads.length; i++) {
    // Get the first email message of a threads
    var message = threads[i].getMessages()[0];
    var content = message.getPlainBody();
    // Get the plain text body of the email message
    // Note that for some types of messages getPlainBody() method may return null
    // in such cases consider using getRawContent() or getBody() methods and parse HTML

    if (content) {
      var date = message.getDate(),
        subject = message.getSubject(),
        sender = message.getFrom(),
        someData = extractData(content,"the", "."),
        name = extractData(content,"Name: ", "\n"),
        comment = content.match(/Comment:\s([^]+?)\n/);
        // You may prefer regex for parsing, then extra validation needed
        comment = (comment && comment[1]) ? comment[1]: 'N/A';
        // Add extra item to parse
      
      sheet.appendRow([date, subject, sender, someData, name, comment]);
      threads[i].addLabel(label);
      //add your label for parsed messages 
      
      Utilities.sleep(500);
    }// End if
  }// End for loop
}