New Email editor: build in “save changes?” prompt

Something I just did on my trackpad had the effect of hitting the back button on my browser and all the changes to my email draft didn't get saved. Would it be possible to force a "save changes?" pop up when someone tries to close or click away from an open draft?

I realise this was my own keyboarding error, but most email drafts either auto-save or prompt you to save when you (intentionally or accidentally) click away.