rmx.mailgw.jp has no MX records.
Question and response
Question
dig rmx.mailgw.jp. MX
Answer
The response has no answer records.
Authority
mailgw.jp. 300 SOA ns2.gao.ne.jp. root.ns2.gao.ne.jp. 2025112501 7200 1800 1209600 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0