spf.xspmail.jp has no MX records.
Question and response
Question
dig spf.xspmail.jp. MX
Answer
The response has no answer records.
Authority
xspmail.jp. 300 SOA dns0.iij.ad.jp. postmaster.iij.ad.jp. 100062 3600 1800 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0