mail.workin.hk has no CNAME records.
Question and response
Question
dig mail.workin.hk. NS
Answer
The response has no answer records.
Authority
workin.hk. 3600 SOA win-7lbvsc0nb6b. hostmaster. 71 900 600 86400 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0