com.au has no MX records.
Question and response
Question
dig com.au. MX
Answer
The response has no answer records.
Authority
com.au. 3600 SOA q.au. hostmaster.donuts.email. 1771766344 7200 900 1209600 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0