internal-api502.heteml.jp has no MX records.
Question and response
Question
dig internal-api502.heteml.jp. MX
Answer
The response has no answer records.
Authority
heteml.jp. 2560 SOA dns0.heteml.jp. hostmaster.heteml.jp. 1772018177 16384 2048 1048576 2560
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0