smtp.blacom.net has no CNAME records.
Question and response
Question
dig smtp.blacom.net. NS
Answer
The response has no answer records.
Authority
blacom.net. 3600 SOA dns1.internetcomunicate.mx. antonio.internetcomunicate.mx. 2026015334 1800 900 2419200 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0