mail231.dopplermta1.com has no MX records.
Question and response
Question
dig mail231.dopplermta1.com. MX
Answer
The response has no answer records.
Authority
dopplermta1.com. 600 SOA pdns13.domaincontrol.com. dns.jomax.net. 2024071800 28800 7200 604800 600
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0