When you compose your first message in Mail you’ll notice the window has shed a little weight. Everything’s still there; it’s all just been rearranged — the BCC menu is now next to the send button and the photo browser is hiding behind the icon that looks like two overlapping squares. And if you’re looking for the account switcher, it’s still in the “from” field; click on your address and you’ll see the selection arrows just like before. (MacLife)