mail1.sencinet.ar has no CNAME records.
Question and response
Question
dig mail1.sencinet.ar. NS
Answer
The response has no answer records.
Authority
sencinet.ar. 154 SOA cobe.sencinet.ar. dns-adm.sencinet.ar. 2026012701 10800 3600 43200 43200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0