QQ企业邮箱的两条MX记录竟然是CNAME：
$ idig mxbiz1.qq.com
mxbiz1.qq.com. 85837 IN CNAME mx1.qq.com.
mx1.qq.com. 37 IN A 64.71.138.87
mx1.qq.com. 37 IN A 64.71.138.88
mx1.qq.com. 37 IN A 64.71.138.90
mx1.qq.com. 37 IN A 64.71.138.80
mx1.qq.com. 37 IN A 64.71.138.81
mx1.qq.com. 37 IN A 64.71.138.82
mx1.qq.com. 37 IN A 64.71.138.83
mx1.qq.com. 37 IN A 64.71.138.84
mx1.qq.com. 37 IN A 64.71.138.85
mx1.qq.com. 37 IN A 64.71.138.86
$ idig mxbiz2.qq.com
mxbiz2.qq.com. 45039 IN CNAME mx2.qq.com.
mx2.qq.com. 600 IN A 112.95.241.33
mx2.qq.com. 600 IN A 112.95.241.34
mx2.qq.com. 600 IN A 112.95.241.35
mx2.qq.com. 600 IN A 112.95.241.36
mx2.qq.com. 600 IN A 112.90.137.245
mx2.qq.com. 600 IN A 112.90.138.89
mx2.qq.com. 600 IN A 112.90.139.247
mx2.qq.com. 600 IN A 112.90.140.86
mx2.qq.com. 600 IN A 112.90.141.240
mx2.qq.com. 600 IN A 112.90.141.252
mx2.qq.com. 600 IN A 112.90.142.115
mx2.qq.com. 600 IN A 112.90.142.116
mx2.qq.com. 600 IN A 112.90.142.53
mx2.qq.com. 600 IN A 112.90.142.54
mx2.qq.com. 600 IN A 112.90.142.55
mx2.qq.com. 600 IN A 112.90.142.56
MX明确不能是CNAME，RFC 2181表述如下：
Section 10.3 of RFC 2181 states:
10.3. MX and NS records
The domain name used as the value of a NS resource record, or part of the value of a MX resource record must not be an alias. Not only is the specification clear on this point, but using an alias in either of these positions neither works as well as might be hoped, nor well fulfills the ambition that may have led to this approach. This domain name must have as its value one or more address records. Currently those will be A records, however in the future other record types giving addressing information may be acceptable. It can also have other RRs, but never a CNAME RR.
对QQ邮箱的这种错误，我相当无语！