New email interface doesn't show count of unread messages for all folders
The new email interface needs to show the quantity of unread messages next to every folder in the left-side folder pane. I need to be able to see every folder which might have unread messages at a glance. The old interface used to do this perfectly (as well as every other webmail interface that I've used), whereas the new interface only shows the count of unread messages in the Inbox folder. This is "User Interface Design 101", and the fault is a rookie mistake which I wouldn't have expected from a company with over two decades of experience in the industry.
This is a deal-breaker for me and is unacceptable. Until this is fixed, I will be using the old interface. If it never gets fixed, I will abandon the Yahoo web email service entirely.

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Justin Tanger commented
This change is wildly incompetent, and I can't fathom how anyone, let alone an entire company, would think this is a good idea. Do the execs and devs actually use their own product? Every time I switch between mailboxes, I have to tap "inbox" and "view all" to actually read the emails I opened the app/mailbox to read? And this "folder" sortation can't even be disabled?? Who TF wants to flip between 5 mailboxes to figure out which folder Yahoo decided to hide the "unread" message in? I assume this change hasn't been rolled out in force or it'd be the #1 complaint here. Literally just started 2 new business accounts, and was going to make one premium, now instead of that I have to transfer it all to Gmail. What a waste of time. Goodbye then.