Apex domains cannot have CNAME records.
Question and response
Question
dig mailrelay.expedient.com. NS
Answer
mailrelay.expedient.com. 5 NS gslb1.dns.expedient.com.
mailrelay.expedient.com. 5 NS gslb2.dns.expedient.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0