sg-mx-2.mail.163.com has no MX records.
Question and response
Question
dig sg-mx-2.mail.163.com. MX
Answer
The response has no answer records.
Authority
163.com. 60 SOA ns4.nease.net. admin.nease.net. 20292168 7200 1800 1209600 60
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0