Mail Preference window wider than the screen

I would try 2 different things:

1. Close Mail and reopen it while pressing the shift key. If this does not fix the problem (I don't think it will but this is easy to try) go to 2.
2. Do an NVRAM/PRAM reset: Reset NVRAM or PRAM on your Mac - Apple Support

Some users have been able to fix this by deleting their signatures: https://discussions.apple.com/thread/8177775

Now, you'll have to use the Tab key to select the Signatures tab and press the space bar to select it. The Signatures tab is right after the Composing tab, so once Composing is highlighted, press tab one more time to select it and press space. You may have to shift-tab first before the "cursor" goes to the tabs at the top of the screen.

you can try putting your cursor on the left side of the mail window until you see a two sided arrow. then use it to drag the window smaller. once you do that, you should be able to drag the entire window into the position that you want it.

sorry, i tried that method. it works for the mail window, but not the mail preferences window.