mx.seed.net.tw has no NS records.
NS records for this zone are defined at seed.net.tw.
NS records for this zone are defined at seed.net.tw.
Question and response
Question
dig mx.seed.net.tw. NS
Answer
The response has no answer records.
Authority
seed.net.tw. 600 SOA dns1.seed.net.tw. dnssrv.du.net.tw. 2016011914 21600 7200 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0