mailing.agh.edu.pl has no CNAME records.
Question and response
Question
dig mailing.agh.edu.pl. NS
Answer
The response has no answer records.
Authority
agh.edu.pl. 1973 SOA ns1.agh.edu.pl. hostmaster.uci.agh.edu.pl. 202603030 86400 7200 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0