Apex domains cannot have CNAME records.
Question and response
Question
dig smtp-hesperia.com. NS
Answer
smtp-hesperia.com. 5 NS ns2.smtp-hesperia.com.
smtp-hesperia.com. 5 NS ns1.smtp-hesperia.com.
Authority
The response has no authority records.
Additional
ns1.smtp-hesperia.com. 5 A 163.5.51.248
ns2.smtp-hesperia.com. 5 A 67.23.253.155
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0