That might be one of the reasons. Get rid of competition by legal means. In my case I keep a copy of K9 Mail 5.6 with the original UI (the reason I choose K9)

That might be one of the reasons. Get rid of competition by legal means. In my case I keep a copy of K9 Mail 5.6 with the original UI (the reason I choose K9) and I sideload it to every device of mine. I'm afraid that I'll have to register an account and what, claim that that K9 is mine?