dns2.cuhk.edu.hk has no MX records.
Question and response
Question
dig dns2.cuhk.edu.hk. MX
Answer
The response has no answer records.
Authority
cuhk.edu.hk. 300 SOA ddi-gm1.itsc.cuhk.edu.hk. hostmaster.cuhk.edu.hk. 201704436 600 300 1814400 300
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0