clientsmx.bulletproof.net has no CNAME records.
Question and response
Question
dig clientsmx.bulletproof.net. NS
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