mail.dacc.cz has no CNAME records.
Question and response
Question
dig mail.dacc.cz. NS
Answer
The response has no answer records.
Authority
dacc.cz. 300 SOA ns1.dacc.cz. domains.dacc.cz. 2025092101 60 30 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0