Yahoo mail hasn't worked well ever since you did some big change a few years ago to it. It works awful on my phone and computer. I doesn't load emails or gets hung up half way. Doesn't let me even sometime write an email! Bad features to easily personalize it (it picks my seen name and doesn't let me pick it).

Please simplify your coding so your email works again. Maybe consider firing your whole development team since they don't seem up to the task. (It's like you want people to not use Yahoo!)