mail.SCO.RU has no CNAME records.
Question and response
Question
dig mail.SCO.RU. NS
Answer
The response has no answer records.
Authority
sco.ru. 6940 SOA ns.sco.ru. admin.sco.ru. 2025092922 14400 600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0