Another issue I have spotted. Indication of new mail in other folders or the inbox is not as robust as the prior application design. After going to my spam folder and leaving that folder open in anticipation of viewing incoming spam for a few days, new mail landing in other folders have no indicators or numbers. This used to be a blue dot beside the folders in the older design ...

I do not know about large sidebar but on the icon only sidebar, if I am in my spam folder for a day or two and a few new emails land in my inbox, there is no number generating over the inbox icon. If I expand the overlay for folders I see numbers for new unread emails in custom folders but NOT from the sidebar itself. There is no indication of new mail. Really, if I am in a folder there should be some indication of unread/new emails in other folders. It has this (numbers) on the custom folders tree overlay when expanded but it doesn't have the on the iconized sidebar itself.

It should have a number on the inbox icon and an indicator on 'Folders' when a custom folder does have a number.