mx2.wolterskluwer.pl has no CNAME records.
Question and response
Question
dig mx2.wolterskluwer.pl. NS
Answer
The response has no answer records.
Authority
wolterskluwer.pl. 3600 SOA ns1.domena.pl. hosting.agnat.pl. 2020080225 7200 1800 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0