mx.OPTORG.RU has no CNAME records.
Question and response
Question
dig mx.OPTORG.RU. NS
Answer
The response has no answer records.
Authority
OPTORG.RU. 2590 SOA ns4.OPTORG.RU. admin.OPTORG.RU. 2025101503 3600 900 3600000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0