I will make another attempt to get through to Yahoo support with the brilliant evidence from Mark_302.
I will add the info from Mark_302 to the case I have with them. Just curious to see what their response might be, although they have been so blatantly obtuse and untruthful in their prior responses, nothing will surprise me.
After that, the only avenue to explore that I can think of is to try and escalate it to the corporate level of Yahoo/AOL or Apollo.
Not interested nor hopeful in pursuing anything with Microsoft based on my prior interactions with them. And, honestly, because I can get no personal benefit because my Outlook 2010 is long out of support
Additional twist - when I try to move emails out of my Inbox to folders, I am limited to under 20 msgs at a time- definitely new limitation from IMAP server and sure to be part of the same implementation