mx.yandex.net has no NS records.
NS records for this zone are defined at yandex.net.
NS records for this zone are defined at yandex.net.
Question and response
Question
dig mx.yandex.net. NS
Answer
The response has no answer records.
Authority
yandex.net. 900 SOA ns1.yandex.net. hostmaster.yandex.net. 2023054790 600 300 1209600 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0