Apex domains cannot have CNAME records.
Question and response
Question
dig mailchimpapp.net. NS
Answer
mailchimpapp.net. 5 NS a4-65.akam.net.
mailchimpapp.net. 5 NS a14-66.akam.net.
mailchimpapp.net. 5 NS a6-66.akam.net.
mailchimpapp.net. 5 NS a7-66.akam.net.
mailchimpapp.net. 5 NS a1-205.akam.net.
mailchimpapp.net. 5 NS a5-65.akam.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0