mx.corp.telmex.net.ar has no CNAME records.
Question and response
Question
dig mx.corp.telmex.net.ar. NS
Answer
The response has no answer records.
Authority
telmex.net.ar. 907 SOA nolldnstmx01apw. ipaddressing.ar.claro.com.ar. 2022042165 10800 3600 360000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0