mx.optinet.hr has no CNAME records.
Question and response
Question
dig mx.optinet.hr. NS
Answer
The response has no answer records.
Authority
optinet.hr. 247 SOA dns1.optima-telekom.hr. dns.optima-telekom.hr. 2025102201 604800 86400 2419200 604800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0