As you aware yahoo groups doesn't maintain the thread format if we reply through emails which creates unnecessary topics instead of adding replies to existing topics (Catalogue of historical novels, for example created unnecessary topics). Now, if a message is orphan then it will be associated to the correct thread if the subject already exists. This is done only @ ponniyinselvan.info not in yahoo groups.
To avoid creating unnecessary topics, please retain the same subject.
And I have a suggestion, can we just do a reply and remove the original message if possible. This would reduce lot of redundant orgininal message content being displayed while reading a thread.