mxproxy601.unisender.ru has no CNAME records.
Question and response
Question
dig mxproxy601.unisender.ru. NS
Answer
The response has no answer records.
Authority
unisender.ru. 3098 SOA ns1.yandexcloud.net. mx.cloud.yandex.net. 1 10800 900 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0