email is missing from my settings on iphone 5c
Believe it or not, you can delete the Mail app from the home screen.

Go to the App Store and see if you can re-download it or install it.

If that doesn’t work, open the setting app and look for any Profiles that restrict apps. Lastly, look in general for restrictions to eliminate Mail.

It’s likely a configuration change that was made to the device. Worst case you can back up the device and then restore it from iTunes if needed.