Right click an open area of the taskbar and click "Properties." Confirm that there is a check in the box labeled "Show Quick Launch," and click "OK." If the quick launch toolbar was previously disabled, you will now see a small group of icons (usually three) on the bottom of the screen.

If you hit WinKey and type Mail, it's the first thing that will be returned in the search results and you can use the context menu that appears beneath it on the right to pin it either to the Taskbar or Start Menu.