mx.supermedia.pl has no CNAME records.
Question and response
Question
dig mx.supermedia.pl. NS
Answer
The response has no answer records.
Authority
supermedia.pl. 323 SOA dns1.supermedia.pl. dns.supermedia.pl. 2026022603 14400 7200 28800 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0