mail2015.apol.com.tw has no NS records.
NS records for this zone are defined at apol.com.tw.
NS records for this zone are defined at apol.com.tw.
Question and response
Question
dig mail2015.apol.com.tw. NS
Answer
The response has no answer records.
Authority
apol.com.tw. 3600 SOA nh468-dns-2200-005.fetnet.net. please_set_email.absolutely.nowhere. 2 15 5 604800 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0