Among several different reasons, the most common reason why your Yahoo mail app is not working is that you forgot to install the app updates on your device. So, before you ask someone why is my yahoo email app not working and how to fix it, the first thing you should do is install the application update on your device. Apart from this, you should also check if the email app is compatible with your device or not. If it is compatible and was working earlier, then you should first uninstall it from your phone and then re-install it once again.