Kudos SteveK08! After a brief test I can confirm that your discovery/workaround works! Cox should fashion some kind of FAQ around this (and send you a check ;) ). I'll admit some trepidation in trying it, since, like others, I have 'mission critical' emails in the former Cox Inbox subfolders (and, indeed, sufficient trepidation to have not tried to move them yet per your workaround -- it is that scary to risk losing them -- and have only done a 'test' of your workaround to confirm it will work).
By way of supplementing your workaround and maybe adding some additional clarity for future readers, I'll share a small part of my experience on the matter. Yep, like others, a couple (3? 4?) hours of unfruitful research before finding your post. And let's just say a few cuss words were involved.
The first thing for people to understand is that Yahoo's concept of 'Inbox' is not quite the same as Cox's former webmail platform's concept of 'Inbox' (and the allowance for subfolders 'underneath' said Inbox). That was my first stumbling block when trying to implement your instructions. In the Yahoo webmail interface you 100% *cannot* (in my experience) create a new subfolder directly underneath their Inbox. You can only create them in the "+ New Folder" area down below. To us longtime Cox/Outlook users, that is *not* intuitive. Thank you very little Cox, Yahoo, and Microsoft.
Again, in my experience (YMMV), no amount of "querying" the IMAP folders in Outlook will produce the opportunity to 'subscribe' to the former Cox Inbox subfolders. They simply do not appear. If somebody has a workaround for this, please post it.
In my Yahoo webmail interface all the former Cox Inbox subfolders appear in the "+ New Folder" area containing an "INBOX/" prefix, e.g., "INBOX/[whatever you named the subfolder]". It is my supposition that the "INBOX/" prefix is what throws the Outlook IMAP query tool off track. Again, nice work Cox, Yahoo, and Microsoft.
Why is that my supposition? Because your workaround according to my testing actually works, and the new folders created in the "+ New Folder" area have no "INBOX/" prefix. How's that for deductive reasoning? ;)
For anybody wanting to replicate my test before proceeding with hours and hours of (potentially risky) manual labor (the reality of which has my wife seriously contemplating abandoning Outlook as an email client), here's what I did (following SteveK08's method):
Logged into Yahoo mail in a web browser. Went to the "+ New Folder" area and created a folder called "New_Folder_Test_For_Outlook". I then clicked and dragged a piece of junk mail from the Yahoo Inbox to this newly created folder. I then went to my Outlook desktop app and did a "Send and Receive" and -- VOILA! -- both the new folder and piece of junk mail appeared! Whoop! Whoop! Not as an Inbox subfolder, mind you, but as a separate folder. I can live with that.
Please don't get me started on the "Bulk" folder the transition magically created and cannot be found in the Yahoo web interface. Or the various flavors of "Sent", "SentMail", "Sent_Items" and what have you, 'cuz then I'm just startin' to sound like a whiner.
Thanks again for your post and workaround SteveK08. Very, very helpful.