mail.d100.nodea.net.pl has no CNAME records.
Question and response
Question
dig mail.d100.nodea.net.pl. NS
Answer
The response has no answer records.
Authority
d100.nodea.net.pl. 57 SOA ns1.nodea.net.pl. hostmaster.d100.nodea.net.pl. 2023102500 100 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0