sm4.hketc.net has no MX records.
Question and response
Question
dig sm4.hketc.net. MX
Answer
The response has no answer records.
Authority
hketc.net. 900 SOA ca.hketc.net. webmaster.hketc.net. 2024041101 10800 1800 1209600 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0