mail.omega.com.pl has no CNAME records.
Question and response
Question
dig mail.omega.com.pl. NS
Answer
The response has no answer records.
Authority
omega.com.pl. 2545 SOA 95.51.156.178. abuse.omega.com.pl. 2022060206 7200 540 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0