mx01.combr.email has no NS records.
NS records for this zone are defined at combr.email.
NS records for this zone are defined at combr.email.
Question and response
Question
dig mx01.combr.email. NS
Answer
The response has no answer records.
Authority
combr.email. 300 SOA ns1.p68.dns.oraclecloud.net. hostmaster.combr.email. 34 3600 600 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0