mail.netonsky.pl has no CNAME records.
Question and response
Question
dig mail.netonsky.pl. NS
Answer
The response has no answer records.
Authority
netonsky.pl. 300 SOA ns1.cal.pl. hostmaster.netonsky.pl. 2025040300 300 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0