Currently I get a lot of e-mails for small changes of the same ticket. It would be very helpful to see those e-mails as a conversation (thread) in GMail or Outlook or Thunderbird. I saw a tip in the answers forum to set the template to include RE: in the subject. however that is not sufficient if you change the subject based on for example status transitions.

A much better and robust solution would be to set the in-reply-to header to the ticket ID or something else that is constant to the ticket.