Apex domains cannot have CNAME records.
Question and response
Question
dig mssm.pl. NS
Answer
mssm.pl. 5 NS ns2.mssm.pl.
mssm.pl. 5 NS ns1.mssm.pl.
mssm.pl. 5 NS ns3.mssm.pl.
Authority
The response has no authority records.
Additional
ns1.mssm.pl. 5 A 85.11.68.25
ns2.mssm.pl. 5 A 85.11.68.26
ns3.mssm.pl. 5 A 85.11.68.27
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0