mail.nipamail.com has no NS records.
NS records for this zone are defined at nipamail.com.
NS records for this zone are defined at nipamail.com.
Question and response
Question
dig mail.nipamail.com. NS
Answer
The response has no answer records.
Authority
nipamail.com. 1800 SOA amy.ns.cloudflare.com. dns.cloudflare.com. 2396989127 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0