That is a connection timed-out error. It means that the servers are not reachable because of an unknown problem. You should check the status of the firewall because in many cases the problem is with the built-in firewall which has triggered some filters and the application can't communicate with servers no more. Another possibility is that the servers you are trying to access are in maintenance mode or disconnected from the Internet. While testing this, you can also disconnect from the Internet, close all your programs and then start the mail client again and perform the same operation.