forward600d.mail.yandex.net has no NS records.
NS records for this zone are defined at mail.yandex.net.
NS records for this zone are defined at mail.yandex.net.
Question and response
Question
dig forward600d.mail.yandex.net. NS
Answer
The response has no answer records.
Authority
mail.yandex.net. 300 SOA ns3.yandex.ru. sysadmin.yandex.ru. 1771913990 900 600 3600000 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0