clientsmx.bulletproof.net has no AAAA records.
Question and response
Question
dig clientsmx.bulletproof.net. AAAA
Answer
The response has no answer records.
Authority
bulletproof.net. 266 SOA ns0.bulletproof.net.au. hostmaster.bulletproof.net.au. 1772589351 108001 3600 604800 600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0