title: Tracking Email replies
body: <p>I have a project that requires us to track whether a reply has been sent for an email. We send mails using Gmail API and its getting send successfully without any issues. But if some user has setup an auto response service and that service has a different subject the gmail treats it as a seperate thread.
  In my backend I get specific threads from users and iterate to check if there is any entry present in the messages having header 'To' as the mail creator. 
  It works as it should but Iam not able to track emails outside the thread. Is there any solution to do this?</p>