The category- and search-folders is a really nice tool to have. But it would be great to see when there are unread mails in the folders (bolded foldername with the number of unread in it).
I couldn’t find any setting to manage this. In my understanding it is a must to have.
It was of course implemented a long time ago to eM Client. It will bold the folder name if there’re some new messages automatically and it will display the number of unread messages with it if the folder is synchronized. You can set folder to synchronize (otherwise only Inbox will synchronize its content automatically) always if you right-click at it, choose Properties, Offline tab and check Download messages for offline use.
If you don’t experience such behavior, you will need to update to the newest version of eM Client (e.g. through menu Help->Check for Update) or from the page www.emclient.com/dist/latest/setup.msi .