mailserver.sinet.ad.jp has no NS records.
NS records for this zone are defined at sinet.ad.jp.
NS records for this zone are defined at sinet.ad.jp.
Question and response
Question
dig mailserver.sinet.ad.jp. NS
Answer
The response has no answer records.
Authority
sinet.ad.jp. 180 SOA dns01.sinet.ad.jp. postmaster.sinet.ad.jp. 2026022001 60 900 259200 180
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0