mx10.X7Z.RU has no CNAME records.
Question and response
Question
dig mx10.X7Z.RU. NS
Answer
The response has no answer records.
Authority
X7Z.RU. 300 SOA ns1.timeweb.RU. dns.timeweb.RU. 1042517 28800 7200 259200 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0