Apex domains cannot have CNAME records.
Question and response
Question
dig encrypt.barracudanetworks.com. NS
Answer
encrypt.barracudanetworks.com. 5 NS ns-1103.awsdns-09.org.
encrypt.barracudanetworks.com. 5 NS ns-1638.awsdns-12.co.uk.
encrypt.barracudanetworks.com. 5 NS ns-196.awsdns-24.com.
encrypt.barracudanetworks.com. 5 NS ns-894.awsdns-47.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0