When I draft an email I always type in the recipients adress first, that way I can find it more easily, when I want to finish writing the email, or I am adding information to it.

However I haven't had the need to click a save button in an email client for so long I couldn't even tell you where it is located, since all clients I have used recently automatically save drafts. I think they save every time you move your mouse, as well as in regular intervalls.