dns0.telstra.net has no MX records.
Question and response
Question
dig dns0.telstra.net. MX
Answer
The response has no answer records.
Authority
telstra.net. 6400 SOA dns0.telstra.net. hostmaster.telstra.net. 2021177198 10800 3600 604800 6400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0