ns15.bbtower.ne.jp has no MX records.
Question and response
Question
dig ns15.bbtower.ne.jp. MX
Answer
The response has no answer records.
Authority
bbtower.ne.jp. 900 SOA pdns10.bbtower.ne.jp. noc.bbtower.ad.jp. 2026020901 3600 1200 3600000 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0