mail.YUS.RU has no NS records.
NS records for this zone are defined at YUS.RU.
NS records for this zone are defined at YUS.RU.
Question and response
Question
dig mail.YUS.RU. NS
Answer
The response has no answer records.
Authority
yus.ru. 3600 SOA isp4.wm.ru. dnsmaster.wm.ru. 2019022884 3600 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0