Apex domains cannot have CNAME records.
Question and response
Question
dig mail.kylos.pl. NS
Answer
mail.kylos.pl. 5 NS ns2.kylos.pl.
mail.kylos.pl. 5 NS ns1.kylos.pl.
Authority
The response has no authority records.
Additional
ns1.kylos.pl. 5 A 195.162.24.10
ns2.kylos.pl. 5 A 5.252.231.125
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0