postfix.har.com has no NS records.
NS records for this zone are defined at har.com.
NS records for this zone are defined at har.com.
Question and response
Question
dig postfix.har.com. NS
Answer
The response has no answer records.
Authority
har.com. 3600 SOA ns-612.awsdns-12.net. awsdns-hostmaster.amazon.com. 2019070801 3600 300 1814400 300
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0