mx.tld.pl has no CNAME records.
Question and response
Question
dig mx.tld.pl. NS
Answer
The response has no answer records.
Authority
tld.pl. 3480 SOA ns1.tld.pl. admin.tld.pl. 2026021918 10800 1800 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0