nttpcnet.nttpc.co.jp has no MX records.
Question and response
Question
dig nttpcnet.nttpc.co.jp. MX
Answer
The response has no answer records.
Authority
nttpc.co.jp. 300 SOA ns1.sphere.ad.jp. dns.sphere.ad.jp. 2026021603 10800 3600 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0