mx.isc.cl has no CNAME records.
Question and response
Question
dig mx.isc.cl. NS
Answer
The response has no answer records.
Authority
isc.cl. 0 SOA ns1.isc.cl. soporte.isc.cl. 2026021901 10800 300 604800 0
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0