AUNTHENTICATE server error

I always get the following error message with my Yahoo account.  “Server says [UNAVAILABLE] AUNTHENTICATE server error please.”  The thing is that I still can receive and send messages but why I get that annoying error message? Could you please help me with that?

Yahoo is notorious for server issues. One thing you can try is to contact Yahoo support and see if there are any current issues when you receive the error. 

Another thing you can check is that you have correct server settings. In Menu > Tools > Accounts, click on the IMAP/POP and SMTP tabs for your account and check that you have the correct port and security policy settings:

Port 587 = Force usage of SSL/TLS

Port 993 = Use SSL/TLS on special port (legacy)

Port 995 = Use SSL/TLS on special port (legacy)

Thanks for your help. Much appreciate it. Following your advice I have changed the server settings. So far I haven’t received the error message since then.