Just my two cents: whenever a I had a problem with a window that did not fit on my screen (and thus the OK button was not visible), I moved the windows upwards beyond the top screen border holding the Alt key, and at the same time clicking and holding with the left mouse key anywhere withing the window I want to move, and then just dragging and dropping it upwards. The window title disappears behind the top border and the "Cancel" and "OK" bottom appear below. I remember using it years ago with gnome, then with Mate DE and I've just tried it with Cinnamon, where I run geary, and it woks!
I hope it helps. By the way, I am great fan and admirer of the software yorba produces, specially Shotwell and geary. Thanks for that!
