mx0.san.attens.net has no NS records.
NS records for this zone are defined at san.attens.net.
NS records for this zone are defined at san.attens.net.
Question and response
Question
dig mx0.san.attens.net. NS
Answer
The response has no answer records.
Authority
san.attens.net. 900 SOA ns-west.cerf.net. rm-hostmaster.ems.att.com. 6 3600 1800 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0