mx.telecom.com.ar has no NS records.
NS records for this zone are defined at telecom.com.ar.
NS records for this zone are defined at telecom.com.ar.
Question and response
Question
dig mx.telecom.com.ar. NS
Answer
The response has no answer records.
Authority
telecom.com.ar. 300 SOA jazzy.arnet.com.ar. dnsmaster.arnet.net.ar. 200911404 7200 3600 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0