smtp-proxy-2-1.hti.pl has no CNAME records.
Question and response
Question
dig smtp-proxy-2-1.hti.pl. NS
Answer
The response has no answer records.
Authority
hti.pl. 3600 SOA dns1.hti.pl. hostmaster.hti.pl. 2019082723 86400 7200 3600000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0