v6spf.xspmail.jp has no NS records.
NS records for this zone are defined at xspmail.jp.
NS records for this zone are defined at xspmail.jp.
Question and response
Question
dig v6spf.xspmail.jp. NS
Answer
The response has no answer records.
Authority
xspmail.jp. 300 SOA dns0.iij.ad.jp. postmaster.iij.ad.jp. 100063 3600 1800 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0