pop3.nap.net.tw has no MX records.
Question and response
Question
dig pop3.nap.net.tw. MX
Answer
The response has no answer records.
Authority
nap.net.tw. 7200 SOA ns1.wonder.net.tw. root.wonder.net.tw. 2025071003 21600 3600 604800 7200
Additional
. 0 OPT ; payload 1432, xrcode 0, version 0, flags 0