o4.mail.sansan.com has no NS records.
NS records for this zone are defined at sansan.com.
NS records for this zone are defined at sansan.com.
Question and response
Question
dig o4.mail.sansan.com. NS
Answer
The response has no answer records.
Authority
sansan.com. 300 SOA ns-241.awsdns-30.com. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0