relay.highradius.com has no NS records.
NS records for this zone are defined at highradius.com.
NS records for this zone are defined at highradius.com.
Question and response
Question
dig relay.highradius.com. NS
Answer
The response has no answer records.
Authority
highradius.com. 900 SOA ns-794.awsdns-35.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0