Group WatchList Realtime mails for the same document under the same conversation/thread in the mail reader

In mail readers that are capable (like GMail, YMail and others), it would be nice if the WatchList Realtime mails regarding a certain document to be grouped under the same conversation/thread to improve the user's experience with the service.

To do this, we can use the MessageID + References and In-Reply-To mail headers.