mx.maildeliver.jp has no CNAME records.
Question and response
Question
dig mx.maildeliver.jp. NS
Answer
The response has no answer records.
Authority
maildeliver.jp. 3600 SOA ns1.gmointernet.com. hostmaster.gmointernet.com. 2025013103 1800 900 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0