I'm using sieve filters and incoming mail is stored in many folders, not only INBOX. So, in Roundcube we're displaying number of unread messages page title, but this number includes only INBOX messages. From my point of view it's useless and for some peaople maybe confusing.
We cannot display number of all unread messages in all folders (because of performance reasons and hard implementation), so I see two solutions:
I think the second is better.