mx1.k2.pl has no CNAME records.
Question and response
Question
dig mx1.k2.pl. NS
Answer
The response has no answer records.
Authority
k2.pl. 21 SOA dns12.ovh.net. tech.ovh.net. 2026012600 86400 3600 3600000 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0