mx.premium.pl has no CNAME records.
Question and response
Question
dig mx.premium.pl. NS
Answer
The response has no answer records.
Authority
premium.pl. 3311 SOA dns.home.pl. admin.home.pl. 1570187690 14400 7200 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0