mail.sfl.com.mx has no CNAME records.
Question and response
Question
dig mail.sfl.com.mx. NS
Answer
The response has no answer records.
Authority
sfl.com.mx. 367 SOA ns152.hostgator.mx. root.mx152.hostgator.mx. 2026022201 86400 7200 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0