## 警告：关于CNAME和MX不能共存的问题

主机记录值 www并不受此影响，主机记录值 www依旧可以使用CNAME来设置解析。

The domain system provides such a feature using the canonical name (CNAME) RR. A CNAME RR identifies its owner name as an alias, and specifies the corresponding canonical name in the RDATA section of the RR. If a CNAME RR is present at a node, no other data should be present; this ensures that the data for a canonical name and its aliases cannot be different. This rule also insures that a cached CNAME can be used without checking with an authoritative server for other RR types.

RFC 1034参考文献