ns2.naverncp.com has no MX records.
Question and response
Question
dig ns2.naverncp.com. MX
Answer
The response has no answer records.
Authority
naverncp.com. 180 SOA ns1.naverncp.com. ns2.naverncp.com. 2020070689 21600 1800 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0