mxg5.impsat.com.ar has no CNAME records.
Question and response
Question
dig mxg5.impsat.com.ar. NS
Answer
The response has no answer records.
Authority
impsat.com.ar. 4428 SOA ns1.gblx.net.ar. hostmaster.impsat.net.ar. 2201103001 7200 3600 604800 21600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0