b.spf.163.com has no MX records.
Question and response
Question
dig b.spf.163.com. MX
Answer
The response has no answer records.
Authority
163.com. 60 SOA ns4.nease.net. admin.nease.net. 20291913 7200 1800 1209600 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0