smtp.customcall.us has no CNAME records.
Question and response
Question
dig smtp.customcall.us. NS
Answer
The response has no answer records.
Authority
customcall.us. 10800 SOA pdns99.ultradns.com. rob\.whritenour.enghouse.com. 2015062154 86400 86400 86400 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0