cuhk.net has no MX records.
Question and response
Question
dig cuhk.net. MX
Answer
The response has no answer records.
Authority
cuhk.net. 600 SOA ddi-gm1.itsc.cuhk.edu.hk. hostmaster.cuhk.edu.hk. 201602069 3600 900 1814400 600
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0