mail.introlan.pl has no CNAME records.
Question and response
Question
dig mail.introlan.pl. NS
Answer
The response has no answer records.
Authority
introlan.pl. 3600 SOA dns1.introlan.pl. biuro.introlan.pl. 2026030301 300 180 36000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0