mx4.netia.pl has no CNAME records.
Question and response
Question
dig mx4.netia.pl. NS
Answer
The response has no answer records.
Authority
netia.pl. 346 SOA ns1.internetia.pl. root.ns1.internetia.pl. 2026022100 86400 7200 2592000 345600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0