I am stumped…
Just setup a new Mac from scratch using iCloud Drive.
I did not know the problem existed on the original machine and am confronted with a problem where when I open Mail > Preferences hat the window extends way beyond the display. When I finally manage to get to the right side of the window I cannot resize it.
I tried deleting various .plist restart etc but it must be something different that synchronized across that I cannot find.
Any help?