POP 3 error mesage

I am getting  a" [POP3} An attempt to connect to email failed. This could be caused by temporary sever unavailability or incorrect setting. Do you want to check the settings?" message. What is causing this and how do I fix?

I had the same problem last month and it turned out to be my fire wall was blocking access. My antivirus program installed a major update and it changed something that blocked my email. I got some IT help that changed a seti g in the firewall and that fixed it.