title: How to reply to thread so the "..." button appears?
body: <p>I do all is required to include a reply in a thread, i.e. <code>in-reply-to</code> and <code>references</code> headers, identical <code>subject</code>, yet messages are received <strong>without</strong> the desired "..." button.</p>
  
  <pre><code>var message = "below should be a ... button to exapnd the thread history";
  
  emps.push(from); // emps is array of employees. add the original sender as a receiver
  
  var base64EncodedEmail = btoa( // encode email "envelope"
              "Content-Type:  text/html; charset=\"UTF-8\"\n" +
              "Content-length: 5000\n" +
              "Content-Transfer-Encoding: message/rfc2822\n" +
              "to: " + emps.join() + "\n" +
              "from: \"" + config.get('my.name') + "\" &lt;"+ config.get('my.email') +"&gt;\n" +
              "In-Reply-To: "+ rfcMsgID + "\n" +
              "References: "+ rfcMsgID + "\n" +
              "subject:" + subject + "\n\n" + // subject is the original message subject
              message
                  ).replace(/\+/g, '-').replace(/\//g, '_');
  var params = { userId: 'me', auth: oauth2Client, resource: { 
      raw: base64EncodedEmail,
      threadId: message.threadId
  }};
  gmail.users.messages.send(params, function(err,message){
      if(err){
          console.log('err from google: %s',err)
      }else{
          console.log('success from google: %s',util.inspect(message))
      }
      callback(err,message)
  });
  </code></pre>
  
  <p>How can I make it work?</p>
  
  <p>(in the pic, the button that I want to show)</p>
  
  <p><a href="https://i.stack.imgur.com/kaW03.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/kaW03.png" alt="this is the button I&#39;m missing"></a></p>