mail.ciberserver.com has no CNAME records.
Question and response
Question
dig mail.ciberserver.com. NS
Answer
The response has no answer records.
Authority
ciberserver.com. 10800 SOA ns1.ciberserver.net. status.ciberconceito.com. 2026020300 3600 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0