Deleting a mail account on only ONE iCloud synced Mac

Solution 1:

The answer turns out to be the no, you can't delete an account on one iCloud synced Mac, without deleting it on the other(s). Beyond leaving said email account disabled, you must go into ~/Library/Mail/V5 in the Finder and uncover the multi-digit-letter folder associated with that account and trash the contents. That's how to reclaim the space occupied (in my case 15GB).

Solution 2:

If you just want to delete the files off of your computer you can go to ~/Library/Mail/V5 through the Go menubar and delete the folder associated with your account.

If you want to not receive any more emails from that address you can right click that emails inbox and select "Take '[email protected]' offline".

If you want to remove that account completely from your computer then select File->Preferences->Accounts. Select your account and click minus. This should only remove your email account from Mail.app