mail.gigaan-demo.awk.jp has no MX records.
Question and response
Question
dig mail.gigaan-demo.awk.jp. MX
Answer
The response has no answer records.
Authority
gigaan-demo.awk.jp. 300 SOA ns.gigaan-demo.awk.jp. m\.saijo.itboost.co.jp. 1679977354 14400 60 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0