POP3 login failed - Sock Error: Host not found

I've got this message with red triangle. However when I checked the email verification, and click 'Test', it said 'All Successful'.

Could anyone kindly advise what should I do to fix this problem?

do you use proxies?

yes, I use proxies (free) from GSA. However after I stopped the operation, and restarted, it's back to normal again. Thank you :-)