As the title states, currently within the Mail window, if you right-click on a mailing list, the first option available is to “Leave Mailing List”. I cannot tell you how many times I have inadvertently left a mailing list when I’m simply trying to select “Mark All as Read”.
Actually, it would be perfect to swap the location of those two items. Place “Mark All as Read” and “Trash All” section first while placing the “Leave Mailing List” at the bottom.