Yes despite all the conjecture on what new rules may be, IMAP is still malfunctioning. I trimmed my AOL Inbox down to 8900 messages, which is the total of Read + Unread. The sync ran for hours, then stopped and reverted at a total of 8700. This abruptly deleted all as usual, reducing the Inbox to 500 and starting over.
And while this slow sync runs all the time, heating up and reducing hardware life, it is impossible to navigate and search in the local email client. That would be the reason why we want Outlook and other local clients. This resource hog also slows the sync of my Outlook Exhange account which used to be instantaneous.
So even giving in to a 10,000 message limit does not help. The Customer Service agents across all providers give invalid and ineffective replies, because Yahoo talks to nobody, but they do act like something has gone wrong.
There was some prior input here from users with some inside-Yahoo knowledge. Is there any real information on this disruption?