sgmail100.mail.163.com has no TXT records.
Question and response
Question
dig sgmail100.mail.163.com. TXT
Answer
The response has no answer records.
Authority
163.com. 60 SOA ns4.nease.net. admin.nease.net. 20292558 7200 1800 1209600 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0