@wilsonms in your original post you said images loaded using the native iPhone mail app, make your mind up.
I work in a time critical role and the bt mail app is a push service, hence why I use it.
Apple mail is a pull service.
Sometimes I receive images, again time critical, so bt mail app tells me and I then open up apple mail to see them!
Mind made up, having to use two apps!
I don't have an iPhone, but a quick Google search reveals the mail app can be configured for push or fetch.