I'm not sure I understand. The threaded view is a presentation to you. When you reply, it is up to the recipient to define whether to have a threaded view also. Am I misunderstanding?

Hi David, you didn't get my question or perhaps i am unable to explain it. let me try once again. suppose i am exchanging mails with client for months and suddenly one day when i reply to him previous mails doesn't show in replies and just only current mail is showing.