mail.DOMENUS.RU has no CNAME records.
Question and response
Question
dig mail.DOMENUS.RU. NS
Answer
The response has no answer records.
Authority
DOMENUS.RU. 2559 SOA ns1.DOMENUS.RU. support.DOMENUS.RU. 2022082504 16384 2048 1048576 2560
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0