spf30.htdb.jp has no MX records.
Question and response
Question
dig spf30.htdb.jp. MX
Answer
The response has no answer records.
Authority
htdb.jp. 300 SOA ns-479.awsdns-59.com. root.htdb.jp. 2026021900 3600 900 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0