inf.bulletproof.net has no MX records.
Question and response
Question
dig inf.bulletproof.net. MX
Answer
The response has no answer records.
Authority
inf.bulletproof.net. 600 SOA ns0.bulletproof.net.au. hostmaster.bulletproof.net.au. 1772654739 10800 3600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0