Using older versions of Outlook for Mac in business environments
Yahoo is still junked up but I created a workaround (alluded to by others) to save my sanity.
My Outlook for the Mac contains 2 accounts: the now screwed up Yahoo (epix.net) account; and an Exchange account for my Outlook.com mail. My Outlook account was never disturbed by the Yahoo craziness. So after getting all my Yahoo folders straightened out in offline mode I created a new folder in my Exchange account called “Epix Inbox”. Then I moved all of my Inbox (Yahoo) mail I wanted to keep into the new Exchange folder and deleted anything remaining.
The next step was to create a Rule in my Yahoo inbox to move all new Yahoo emails into my new Exchange folder (Epix Inbox). I followed up by moving other Yahoo folders containing mail I wanted to keep to the protection provided by Exchange.
Long way around the horn perhaps, and definitely not the solution, but it works fine. Plus it was an opportunity to do some long overdue email cleanup. If even Yahoo fixes this, I not sure I would ever trust them again as I am now convinced this is a Yahoo problem.