mail.CLOUD4BOX.RU has no CNAME records.
Question and response
Question
dig mail.CLOUD4BOX.RU. NS
Answer
The response has no answer records.
Authority
CLOUD4BOX.RU. 2373 SOA ns1.contell.RU. tech.contell.RU. 2021140871 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0