spf.nttcom.ne.jp has no MX records.
Question and response
Question
dig spf.nttcom.ne.jp. MX
Answer
The response has no answer records.
Authority
nttcom.ne.jp. 300 SOA ns2.nttcom.ne.jp. root.nttcom.ne.jp. 2025102801 10800 1800 2419200 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0