Apex domains cannot have CNAME records.
Question and response
Question
dig flowmailer.net. NS
Answer
flowmailer.net. 5 NS ns3.flowmailer.net.
flowmailer.net. 5 NS ns4.flowmailer.net.
Authority
The response has no authority records.
Additional
ns3.flowmailer.net. 5 A 139.162.156.32
ns4.flowmailer.net. 5 A 93.119.10.166
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0