mx.biaman.pl has no CNAME records.
Question and response
Question
dig mx.biaman.pl. NS
Answer
The response has no answer records.
Authority
biaman.pl. 3357 SOA dns.man.bialystok.pl. root.dns.man.bialystok.pl. 2025121500 10800 1200 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0