mx1.cmd.com.ar has no NS records.
NS records for this zone are defined at cmd.com.ar.
NS records for this zone are defined at cmd.com.ar.
Question and response
Question
dig mx1.cmd.com.ar. NS
Answer
The response has no answer records.
Authority
cmd.com.ar. 900 SOA ns-1317.awsdns-36.org. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0