Yahoo users need to authenticate using an app password instead of their email password.
To generate an app password:
- Sign in to Yahoo Mail.
- Navigate to "Account Info".
- Go to the "Account security" settings.
- At the bottom of the page, choose the option to "Generate app password" or "Manage app passwords".
- Generate a new app password.
- Try authenticating again with Nylas, using the newly-generated password.
This approach is also appropriate for users who have two-factor authentication enabled.
For more details, see Generate third-party app passwords in Yahoo Help.