Let’s say you have 2 main subfolders below the Inbox. Aggregating unread items via a Search Folder Outlook doesn’t automatically combine the total of unread items of collapsed folders as shown above but you can still achieve by defining Search Folders. If that is for multiple levels, you can of course define multiple Search Folders. You must decide however at which folder level it makes sense to see the combined total of unread items. However, you can still achieve something similar by using Search Folders.

No, there is no way to do that in Outlook. Is there a way to make the parent folder show the combined amount of unread items in any of the subfolders? Even these folder trees are expanded, I would have to scroll in order to see them all. Usually I keep this folder structure collapsed but then I can't see if a message arrived in any of these subfolders. In addition, I'm using rules to automatically move messages to their corresponding folder.

I'm organizing my emails into various subfolders which have subfolders of their own again.