mail.studio-o.com has no CNAME records.
Question and response
Question
dig mail.studio-o.com. NS
Answer
The response has no answer records.
Authority
studio-o.com. 2852 SOA ns1.studio-o.com. admin.studio-o.com. 2025041101 43200 120 2419200 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0