primary.us.email.fireeyecloud.com has no CNAME records.
Question and response
Question
dig primary.us.email.fireeyecloud.com. NS
Answer
The response has no answer records.
Authority
fireeyecloud.com. 1383 SOA bonnie.ns.cloudflare.com. dns.cloudflare.com. 2397141198 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0