mail7419.e.firstmarkservices.com has no NS records.
NS records for this zone are defined at e.firstmarkservices.com.
NS records for this zone are defined at e.firstmarkservices.com.
Question and response
Question
dig mail7419.e.firstmarkservices.com. NS
Answer
The response has no answer records.
Authority
e.firstmarkservices.com. 900 SOA ns1.acoustic-adm.com. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0