spf01.isize.com has no MX records.
Question and response
Question
dig spf01.isize.com. MX
Answer
The response has no answer records.
Authority
isize.com. 300 SOA ns1.x.recruit.co.jp. postmaster.x.recruit.co.jp. 2026022401 3600 900 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0