mail.SN.RU has no CNAME records.
Question and response
Question
dig mail.SN.RU. NS
Answer
The response has no answer records.
Authority
SN.RU. 10800 SOA ns5.salenames.RU. noc.salenames.RU. 2025111801 10800 3600 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0