_spf.mwprem.net has no MX records.
Question and response
Question
dig _spf.mwprem.net. MX
Answer
The response has no answer records.
Authority
mwprem.net. 3600 SOA mwns1.customer.ne.jp. host-plan-ac.ntt.com. 1613490392 3600 1800 3628800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0