mx1.centuria.pl has no CNAME records.
Question and response
Question
dig mx1.centuria.pl. NS
Answer
The response has no answer records.
Authority
centuria.pl. 589 SOA ns1-201.azure-dns.com. linux.centuria.pl. 2021110913 3600 600 1209600 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0