mxr.wolterskluwer.pl has no MX records.
Question and response
Question
dig mxr.wolterskluwer.pl. MX
Answer
The response has no answer records.
Authority
wolterskluwer.pl. 3600 SOA ns1.domena.pl. hosting.agnat.pl. 2020080222 7200 1800 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0