mx.dinst.pl has no CNAME records.
Question and response
Question
dig mx.dinst.pl. NS
Answer
The response has no answer records.
Authority
dinst.pl. 464 SOA ns0.pttk.pl. admin.dinst.pl. 2022101924 604800 86400 2419200 604800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0