No such host is known. The name you used is not an official host name or alias. This is not a software error, another type of name server request may be successful.
Check that you have a name server(s) and/or host table configured. If you are using a name server(s), check whether the server host(s) are up (e.g. try to ping the server(s)). You could also try to resolve another host name you know should work, to check if the name resolution server application is running.
No connection could be made because the target machine actively refused it. This usually results from trying to connect to a service that is inactive on the foreign host.
So either you tried to connect the wrong host, or the service (SMTP, POP3, IMAP) you're trying to contact isn't available. Check the destination address you are using. If you used a host name, did it resolve to the correct address? It's also possible that the remote services use a different port number.
A connect or send request failed because the connected server did not respond properly after a period of time. Check, if the destination address is a valid IP address. If you used a host name, did it resolve to the correct address?
An operation on a socket or pipe was not performed because the system lacked sufficient buffer space or because a queue was full.
This error indicates a shortage of resources on your system. It can occur if you're trying to run too many applications (of any kind) simultaneously on your machine. If it persists, exit Windows or reboot your machine to remedy the problem.