Apex domains cannot have CNAME records.
Question and response
Question
dig mail.cyberneticos.com. NS
Answer
mail.cyberneticos.com. 5 NS cyberb.cyberneticos.com.
mail.cyberneticos.com. 5 NS cybera.cyberneticos.com.
Authority
The response has no authority records.
Additional
cybera.cyberneticos.com. 4 A 164.138.209.74
cyberb.cyberneticos.com. 4 A 164.138.209.71
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0