mx01.agnat.pl has no CNAME records.
Question and response
Question
dig mx01.agnat.pl. NS
Answer
The response has no answer records.
Authority
agnat.pl. 2836 SOA ns1.agnat.pl. bok.domena.pl. 2006054465 7200 1800 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0