We pick l.root-servers.net, one of the 13 root servers (1), and ask it about boletimdocontribuinte.pt and learn that pt is delegated to eight name servers (2), so we ask ns-pt.nlnetlabs.nl where we learn that boletimdocontribuinte.pt is delegated to two name servers, including ns1.eurotux.com (3), so we ask that one and get the following answer:
All of the three host names that point to the IP number 188.8.131.52 point only to that ip number.
The IP number 184.108.40.206 only
All of the three host names that point only to the IP number 220.127.116.11 use the two name servers ns1 and ns3.eurotux.com together, hereafter referred to as "name server group 1". Worth noting is that three of the domains that use name server group 1 point only to the IP number 18.104.22.168.
The three name servers ns1.eurotux.com, ns3.eurotux.com and a.ns.mni.pt together