I have an iPhone 5C running iOS10.1.1. (See that 10.2.1 is available but I have not installed it yet.) Last night I noticed that the bottom row of icons (the non-moveable ones) looked "sparse". On exploration this morning, somehow Mail and Music have disappeared. Have no idea why and little idea about what to do, except I know I at least want Mail back. At this very second I am waiting for my neighbor to take me to the hospital for a procedure on one of my vertebrae, so don't have time to attempt a reload at the moment (if I remember how), but does anyone have any suggestions? On how to fix the problem, and why it happened in the first place?