mailc75.carrierzone.com has no CNAME records.
Question and response
Question
dig mailc75.carrierzone.com. NS
Answer
The response has no answer records.
Authority
carrierzone.com. 986 SOA ns1.carrierzone.com. admin.carrierzone.com. 2017082764 86400 3600 3600000 345600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0