Your email functions UX/UI is less and less functional and more and more useless. I do not know why in the sent hisotory I can not see the message to which I replied and why I can not reply to email twice. Each time I want to reply again I am sending it to myself, I need to start a new email.
If you want people to stop using yahoo mail you can just say so, there is no need to make it more difficult for the user.
Monika Luka shared this idea