I really liked the default email app that used to come with Android. The bare-bones interface used to get the job done without any hassle.
Unfortunately, Google decided to kill it with Lollipop and integrated all other email services with Gmail. This was an unwelcome decision - I like to keep my inboxes separate... I tried some other apps on the play store, but most didn't work well, and the ones which did were filled with ads or required payment for basic features.
So I borrowed my friend's phone which still ran KitKat, and extracted the apk for the stock email app. This is the last working version of the app ever released. It doesn't have the material design icon, but that doesn't really matter...
You can download it here.