mx.tds.net has no NS records.
NS records for this zone are defined at tds.net.
NS records for this zone are defined at tds.net.
Question and response
Question
dig mx.tds.net. NS
Answer
The response has no answer records.
Authority
tds.net. 3600 SOA pv-dnsm.dns.tds.net. hostmaster.tds.net. 2025041776 21600 3600 604800 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0