mx.caraocar.com has no NS records.
NS records for this zone are defined at caraocar.com.
NS records for this zone are defined at caraocar.com.
Question and response
Question
dig mx.caraocar.com. NS
Answer
The response has no answer records.
Authority
caraocar.com. 3600 SOA dns.caraocar.com. hostmaster.caraocar.com. 1232835003 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0