If you searched for this article, most likely you've got the following error message while trying to connect you Yahoo! mail account to LiveAgent:
Authentication failed, please check your username/password. Other possible reason could be the server is blocking the IP/country LiveAgent is accessing the email account from. As LiveAgent servers are hosted in Slovakia, Germany, UK and USA, please make sure the email server is not blocking access from these countries.
If you are 100% sure that you are providing correct login credentials and your mail account is no restricted for any country you will need to check the "Account security" section of your Yahoo! account which can be found on the following link - https://login.yahoo.com/account/security Enable the "Allow apps that use less secure sign-in" option and then try to re-connect it in LiveAgent.