You sure you didn't uninstall your
Mail application? If you did, you wouldn't have
Calendar,
People,
Messaging apps either. Well all you have to do to get it back is to download it again from the Windows Store. Open up the Charms bar, press search, and type "
Mail, Calendar,
People,
Messaging". You should see it automatically and click on it. There are two choices here. If you do not see an "
Install" button:
...it means that you have it installed. If you do see an "Install" button, then you did uninstall it but pressing the button will give you the
Mail app back and will be available in the Start screen.
If you have it installed but you can't find the Mail app anywhere, uninstall
"Mail, Calendar,
People,
Messaging".
From there just search for it in the Windows Store and press the "
Install" button. Not that hard.