mail1.mailer.twinfield.com has no NS records.
NS records for this zone are defined at twinfield.com.
NS records for this zone are defined at twinfield.com.
Question and response
Question
dig mail1.mailer.twinfield.com. NS
Answer
The response has no answer records.
Authority
twinfield.com. 1800 SOA jihoon.ns.cloudflare.com. dns.cloudflare.com. 2398856459 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0