Apex domains cannot have CNAME records.
Question and response
Question
dig ns.campaign.adobe.com. NS
Answer
ns.campaign.adobe.com. 5 NS ns-1513.awsdns-61.org.
ns.campaign.adobe.com. 5 NS ns-83.awsdns-10.com.
ns.campaign.adobe.com. 5 NS ns-733.awsdns-27.net.
ns.campaign.adobe.com. 5 NS ns-1742.awsdns-25.co.uk.
Authority
The response has no authority records.
Additional
ns-1742.awsdns-25.co.uk. 2 A 205.251.198.206
ns-1742.awsdns-25.co.uk. 2 AAAA 2600:9000:5306:ce00:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0