correo.redunda.com has no NS records.
NS records for this zone are defined at redunda.com.
NS records for this zone are defined at redunda.com.
Question and response
Question
dig correo.redunda.com. NS
Answer
The response has no answer records.
Authority
redunda.com. 10800 SOA ns1.gandi.net. hostmaster.gandi.net. 1772668800 10800 3600 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0