smtp52.bigcommerce.net has no CNAME records.
Question and response
Question
dig smtp52.bigcommerce.net. NS
Answer
The response has no answer records.
Authority
bigcommerce.net. 1313 SOA dns1.p03.nsone.net. hostmaster.nsone.net. 1649182293 43200 7200 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0