This application doesn't appear to be available anymore, therefore its compatibility is questionable since new operating systems have been released, but the application didn't receive any updates at all, making impossible to troubleshoot errors.
I strongly recommend to use another application instead of the Yahoo Mail one because you will have better support and besides that, they're all updated.
Take the settings from here and use an application listed on that page as well: https://help.yahoo.com/kb/SLN22038.html
