es2.3.proofhubmail.com has no NS records.
NS records for this zone are defined at proofhubmail.com.
NS records for this zone are defined at proofhubmail.com.
Question and response
Question
dig es2.3.proofhubmail.com. NS
Answer
The response has no answer records.
Authority
proofhubmail.com. 900 SOA ns-791.awsdns-34.net. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0