mx1au.supremebox.com has no CNAME records.
Question and response
Question
dig mx1au.supremebox.com. NS
Answer
The response has no answer records.
Authority
supremebox.com. 2481 SOA dns1.supremebox.com. hostmaster.supremebox.com. 1772503507 16384 2048 1048576 2560
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0