sau.net.au has no MX records.
Question and response
Question
dig sau.net.au. MX
Answer
The response has no answer records.
Authority
sau.net.au. 1800 SOA jimmy.ns.cloudflare.com. dns.cloudflare.com. 2398155371 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0