How to fix
In general, if you are unable to authenticate your Yahoo email account using your username and password, we would always suggest first making absolutely certain that both your Yahoo username and Yahoo password are being inputted correctly.
The message you are seeing should state the following:
- [AUTHENTICATIONFAILED] AUTHENTICATE Invalid credentials
It may also be due to a new security feature in Yahoo whereby Yahoo disables access from what they call "less secure apps". It does not mean that Mailbird is not secure (we rigorously connect using full encryption), so it's simply how Yahoo defines a non-Yahoo application which is connecting using a username and password.
In order to allow Mailbird to connect to Yahoo, you can enable access by following the steps at the bottom of this guide: