mx2b.supremebox.com has no CNAME records.
Question and response
Question
dig mx2b.supremebox.com. NS
Answer
The response has no answer records.
Authority
supremebox.com. 2560 SOA dns1.supremebox.com. hostmaster.supremebox.com. 1772583907 16384 2048 1048576 2560
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0