mx.korbank.pl has no CNAME records.
Question and response
Question
dig mx.korbank.pl. NS
Answer
The response has no answer records.
Authority
korbank.pl. 148 SOA dns.korbank.pl. hostmaster.korbank.pl. 2025091528 900 300 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0