Hi Mern, by doing the following, which is maximising the window manually and NOT by click on the expanding icon in the upper lefthand corner, this may solve your problem.
Open any email in its own window by double-clicking it in its folder.
Make sure the window is not maximized.
Move the email window so that its top left corner coincides with the top left corner of your screen.
Grab the handle in the window's bottom right corner with the mouse and drag it to the bottom right corner of the screen.
Close the message window.