mx.donpac.ru has no CNAME records.
Question and response
Question
dig mx.donpac.ru. NS
Answer
The response has no answer records.
Authority
donpac.ru. 1758 SOA ns0.donpac.ru. dnsmaster.donpac.ru. 2025090401 43200 7200 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0