bradstewart: I'm using the default KitKat email client (not Gmail) with an account as well as an exchange one and multiple messages are not being threaded.

I use it aswell, Have my own domain with

Good gui and no issues. But we cant expect Outlook 2013 from a phone..

Lack of threading is a plus for me. For work purposes it makes life considerably easier.

K9 Mail does threading.

But I don't want threading! I'm perfectly happy with the stock 4.4 app which I was suggesting to the OP as he also doesn't like threading.