mail.corp.mchost.RU has no CNAME records.
Question and response
Question
dig mail.corp.mchost.RU. NS
Answer
The response has no answer records.
Authority
corp.mchost.RU. 1806 SOA dns1.mchost.RU. info.mchost.RU. 2023062202 10800 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0