mail.suntec.awk.jp has no CNAME records.
Question and response
Question
dig mail.suntec.awk.jp. NS
Answer
The response has no answer records.
Authority
suntec.awk.jp. 175 SOA ns.suntec.awk.jp. system.egg.co.jp. 1623895279 14400 60 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0