mail.comclark.com has no CNAME records.
Question and response
Question
dig mail.comclark.com. NS
Answer
The response has no answer records.
Authority
comclark.com. 2047 SOA ns1.comclark.com. hostmaster.comclark.com. 2013061202 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0