To close the Mail app: If the basic solution did not work, you can try the next methods.Another simple way of fixing the email app not working problem is by restarting your i Device.
I had same thing tried everything, deleting accounts, adding again, turning off ipad numerous times.
I had open email on safari.i went back in and open the email again on safari and the actually logged out before X out.
It can be infuriating if the Mail app suddenly stops working(Sending or Receiving Emails on Gmails/Outlook/Yahoo) and you do not know what is wrong with it after updating to i OS 10.0.
Since the Mail app is essential for your work, it is important to fix it as soon as you can.
You can also force reboot your device which is better than a simple restart.
To do force reboot, simply press and hold the Sleep/Wake button and the Home button until the Apple logo appears.
How to sync calendar with i Phone can be implemented easily.
There are different exchanges for calendar sync and the choice depends upon the user.
Before you proceed, make sure that your i Phone 7 Plus or i Pad is connected to the internet.