Apex domains cannot have CNAME records.
Question and response
Question
dig campaign.adobe.com. NS
Answer
campaign.adobe.com. 5 NS ns-1852.awsdns-39.co.uk.
campaign.adobe.com. 5 NS ns-182.awsdns-22.com.
campaign.adobe.com. 5 NS ns-997.awsdns-60.net.
campaign.adobe.com. 5 NS ns-1122.awsdns-12.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0