Contrary to what I expect, this server isn't visible in the servers list of my client. What can I do to make it visible ? Or should i connect by directly entering its IP address ?
You can't connect to 4.1 server because the 4.2 version isn't retro-compatible with older versions, due to major changes (weapons available, skins, etc.).
Since January 1st, 2014, masters for the 4.1 servers are even shut down, so it's became impossible to list every servers using this version. You should move forward and play only on 4.2 servers :)