mx.trulysustainable.net has no MX records.
Question and response
Question
dig mx.trulysustainable.net. MX
Answer
The response has no answer records.
Authority
trulysustainable.net. 3600 SOA dns.trulysustainable.net. hostmaster.trulysustainable.net. 1414762800 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0