I cannot send or receive emails the message I get when I try to says error in internet preferences pane!

When I try to send or receive emails I get a message saying 'Internet Accounts preferences cannot connect to the Yahoo account btinternet.com. The version of mail I am using is 7.3

I have tried opening keychain access but am not confident in the instructions. Please can anyone help. The actual internet connection is giving a green light mail was able to connect to the internet. Thank you