mx.optorg.RU has no MX records.
Question and response
Question
dig mx.optorg.RU. MX
Answer
The response has no answer records.
Authority
optorg.RU. 119 SOA ns4.optorg.RU. admin.optorg.RU. 2025101503 3600 900 3600000 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0