smtp.blacom.com.mx has no CNAME records.
Question and response
Question
dig smtp.blacom.com.mx. NS
Answer
The response has no answer records.
Authority
blacom.com.mx. 2856 SOA www.blacom.com.mx. antonio.internetcomunicate.mx. 2025033104 1800 900 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0