mx1.syd07.bulletproof.net has no MX records.
Question and response
Question
dig mx1.syd07.bulletproof.net. MX
Answer
The response has no answer records.
Authority
bulletproof.net. 300 SOA ns0.bulletproof.net.au. hostmaster.bulletproof.net.au. 1772589179 108001 3600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0