Using New Outlook on Windows for professional communication and productivity
The fix is simple. Dump any sort of Microsoft email clients and switch to a third part solution. I switched to MailBird a couple of months ago, and couldn't be happier. All my accounts work, and Yahoo works flawlessly. Microsoft has had problems with Yahoo's email for years, and still does. The third party developers don't seem to have an issue with Yahoo though. Microsoft can't get email right for whatever reason, and it may be by design.