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. 2347 SOA ns4.optorg.ru. admin.optorg.ru. 2025101503 3600 900 3600000 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0