I had to solve this problem: someone pointed his domain name to the IP of my server, and then by default NGINX returns the 200 code and Success default page for new domain names. So i searched the way to configure NGINX to return only 404 error code when the domain is not hosted in my server.

I'm not an specialist on this area, but a novel sysadmin i had to solve this situation and it took to me almost 10 hours (2 days) to get it well solved. I want to share what i learned with you. I need to express my thanks to the great customer support team at clouding.io (my BEST cloud hosting provider).