We have discovered an issue with connecting emails from Yahoo to Mailead. Recently Yahoo stopped allowing users to create an app. It’s why Mailead can't directly integrate with them.
To connect a Yahoo account, you need to create an app password and use that instead of your regular email password (refer to https://help.yahoo.com/kb/SLN4075.html). If you can successfully create an app password, it should work. However, Yahoo has been experiencing issues recently with app password generation.