smtp.db-center.jp has no NS records.
NS records for this zone are defined at db-center.jp.
NS records for this zone are defined at db-center.jp.
Question and response
Question
dig smtp.db-center.jp. NS
Answer
The response has no answer records.
Authority
db-center.jp. 600 SOA ns1.db-center.net. webmaster.iqnet.co.jp. 2026012001 3600 600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0