spf-d.mail.163.com has no NS records.
NS records for this zone are defined at 163.com.
NS records for this zone are defined at 163.com.
Question and response
Question
dig spf-d.mail.163.com. NS
Answer
The response has no answer records.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0