Apex domains cannot have CNAME records.
Question and response
Question
dig powermail.be. NS
Answer
powermail.be. 5 NS ns4.european-server.com.
powermail.be. 5 NS ns3.european-server.com.
powermail.be. 5 NS ns1.european-server.eu.
Authority
The response has no authority records.
Additional
ns3.european-server.com. 5 A 83.217.73.172
ns4.european-server.com. 5 A 86.39.202.67
ns3.european-server.com. 5 AAAA 2a00:1c98:0:0:0:0:53:1
ns4.european-server.com. 5 AAAA 2001:1598:0:101:0:0:0:3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0