Thanks for that recommendation, as I've made good progress with it! I was able to remove one of the two duplicate email addresses in Favorites, and when checking under Account Settings>Email Accounts, there are no longer any numbers like (1) and (2) after that email address anymore. But there is still the one duplicate email address under Favorites, and when I do the right click that you've recommended to close it, the option to close that email address in Favorites is grayed out.