mx.tw-ink.com has no CNAME records.
Question and response
Question
dig mx.tw-ink.com. NS
Answer
The response has no answer records.
Authority
tw-ink.com. 3306 SOA dns.tw-ink.com. hostmaster.tw-ink.com. 1180367323 43200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0