Apex domains cannot have CNAME records.
Question and response
Question
dig mx.spoje.net. NS
Answer
mx.spoje.net. 5 NS ns2.spoje.net.
mx.spoje.net. 5 NS ns3.spoje.net.
mx.spoje.net. 5 NS ns.spoje.net.
Authority
The response has no authority records.
Additional
ns.spoje.net. 5 A 88.208.121.2
ns2.spoje.net. 5 A 213.151.89.1
ns3.spoje.net. 5 A 88.146.242.186
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0