Just recently, Yahoo has enabled a new protection protocol for all Yahoo accounts. This protection prohibits signing in your account from a third party email app, that’s why you can't log in your Yahoo account by ASUS Email app.
Try to sign in via ASUS Email app by following steps:
- Log in your Yahoo account via a browser using this link:
https://login.yahoo.com/account/
security#other-apps - Turn on Allow apps that use less secure sign in.
- Launch ASUS Email then try to sign in your Yahoo account.
