Apex domains cannot have CNAME records.
Question and response
Question
dig ascentymail.com. NS
Answer
ascentymail.com. 5 NS c.dns.ascenty.com.
ascentymail.com. 5 NS a.dns.ascenty.com.
ascentymail.com. 5 NS b.dns.ascenty.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0