mail.iweb.pl has no CNAME records.
Question and response
Question
dig mail.iweb.pl. NS
Answer
The response has no answer records.
Authority
iweb.pl. 1175 SOA dns.iweb.pl. pit.iweb.pl. 2022102210 43200 7200 1209600 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0