Exchange mail won't push through unless I open the mail app. Yes push is selected.
IphoneXS current update.
Contact your Exchange administrator if you are not getting Exchange Mail pushed. I'm guessing that you did configure the mail account by selecting Exchange when you first added it to the iPhone. The Exchange administrator controls the iPhone being connected to the iPhone and it has to have a constant connection for it to Push correctly. They know how to troubleshoot those issues.