A watch app is key. I wont be able to make this my main email until that happens. Also, a personal preference is to move to the next message by swiping. On this app, you have to touch the arrow at the top of the screen which is kind of awkward on big phones when you have small hands.
As with many new email apps, this is a good start and Im looking forward to further improvements. I like the security and the screen is very easy to read.
TheMagicNumber about Email - Edison Mail, v1.4.1