mail.plus.hr has no CNAME records.
Question and response
Question
dig mail.plus.hr. NS
Answer
The response has no answer records.
Authority
plus.hr. 3544 SOA ns1.phg.hr. server.plus.hr. 2026020500 28800 7200 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0