mail.clearcable.net has no CNAME records.
Question and response
Question
dig mail.clearcable.net. NS
Answer
The response has no answer records.
Authority
clearcable.net. 3548 SOA ns1.clearcable.ca. hostmaster.clearcable.ca. 1772522982 10800 3600 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0