Apex domains cannot have CNAME records.
Question and response
Question
dig prod.cloud.synchronoss.net. NS
Answer
prod.cloud.synchronoss.net. 1 NS ns-1261.awsdns-29.org.
prod.cloud.synchronoss.net. 1 NS ns-19.awsdns-02.com.
prod.cloud.synchronoss.net. 1 NS ns-897.awsdns-48.net.
prod.cloud.synchronoss.net. 1 NS ns-1876.awsdns-42.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0