From your Inbox, you can now quickly view just the messages that haven't been responded to. This allows you to quickly clear out your inbox.
You'll find this checkbox next to "Unread" at the top of the page.
No more 'Marking Unread' to keep track of to-do's
An inbox shouldn't be a to-do list.
Maybe you've fallen into the habit of leaving messages as "unread" to keep track of what needs to be responded to. You no longer have to lean on this habit. After all, you have read that message, haven't you?
Undoubtedly, some messages will require digging before a response can be sent.
When you have several of these messages that you're actively looking into -- and can't remember which you've responded to -- you can now quickly bubble them all to the top. Do this when its time to respond to everything outstanding, regardless of whether or not they've been read.