dynamic.isl.net.tw has no MX records.
Question and response
Question
dig dynamic.isl.net.tw. MX
Answer
The response has no answer records.
Authority
dynamic.isl.net.tw. 86400 SOA dns.isl.net.tw. root.isl.net.tw. 2003111202 14400 3600 604800 86400
Additional
. 0 OPT ; payload 1432, xrcode 0, version 0, flags 0