mx.korean456.com has no NS records.
NS records for this zone are defined at korean456.com.
NS records for this zone are defined at korean456.com.
Question and response
Question
dig mx.korean456.com. NS
Answer
The response has no answer records.
Authority
korean456.com. 3600 SOA dns.korean456.com. hostmaster.korean456.com. 1742379088 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0