mx1.perfect-net.pl has no CNAME records.
Question and response
Question
dig mx1.perfect-net.pl. NS
Answer
The response has no answer records.
Authority
perfect-net.pl. 74 SOA ns1.perfect-net.pl. dns.perfect-net.pl. 2025120300 21600 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0