qq-b.mail.qq.com has no CNAME records.
Question and response
Question
dig qq-b.mail.qq.com. NS
Answer
The response has no answer records.
Authority
mail.qq.com. 47 SOA qq.com. webmaster.qq.com. 1768972738 300 600 86400 180
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0