smtp.comclark.com has no CNAME records.
Question and response
Question
dig smtp.comclark.com. NS
Answer
The response has no answer records.
Authority
comclark.com. 1371 SOA ns1.comclark.com. hostmaster.comclark.com. 2013061203 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0