mx.bizmail.nifty.com has no NS records.
NS records for this zone are defined at bizmail.nifty.com.
NS records for this zone are defined at bizmail.nifty.com.
Question and response
Question
dig mx.bizmail.nifty.com. NS
Answer
The response has no answer records.
Authority
bizmail.nifty.com. 900 SOA odns0.nifty.ad.jp. hostmaster.nifty.ad.jp. 202602260 3600 900 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0