mail.centex.net has no NS records.
NS records for this zone are defined at centex.net.
NS records for this zone are defined at centex.net.
Question and response
Question
dig mail.centex.net. NS
Answer
The response has no answer records.
Authority
centex.net. 900 SOA ns1.centex.net. please_set_email.absolutely.nowhere. 2010531303 10800 3600 2592000 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0