mail.hgdata.sk has no CNAME records.
Question and response
Question
dig mail.hgdata.sk. NS
Answer
The response has no answer records.
Authority
hgdata.sk. 112436 SOA ns1.hgdata.sk. hostmaster.hgdata.sk. 2025093603 86400 7200 3600000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0