mx2.mail.aliyun.com has no MX records.
Question and response
Question
dig mx2.mail.aliyun.com.gds.alibabadns.com. MX
Answer
The response has no answer records.
Authority
gds.alibabadns.com. 600 SOA gdsns1.alibabadns.com. none. 2018122017 1800 600 3600 360
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0