ptr1.twnic.net.tw has no MX records.
Question and response
Question
dig ptr1.twnic.net.tw. MX
Answer
The response has no answer records.
Authority
twnic.net.tw. 1800 SOA dns.nic.net.tw. snw.twnic.net.tw. 1771808401 7200 1800 2419000 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0