[dns-operations] MX CNAMEs

Mark Andrews marka at isc.org
Fri Dec 26 07:39:21 UTC 2014

Just because it works some of the time that doesn't mean that it will work all of the time. The cname rule is there to cope with multiple mx records with different preferences.  It also comes into play when there is a misconfiguration with a single mx.
The visible effect is that you get a mail loop rather than queuing of the email or a bounce. 

On 26/12/2014, at 17:17, 风河 <news at windwrite.com> wrote:

> I was thinking MX should not be a CNAME record.
> But these two are broken the rules, and they seem work just fine?
> 2008.sina.com.        52    IN    MX    10 mx.2008.sina.com.
> mx.2008.sina.com.    8    IN    CNAME    freemx1.sinamail.sina.com.cn.
> freemx1.sinamail.sina.com.cn. 8    IN    A
> And,
> mail.china.com.        391    IN    CNAME    mail.china.com.cachecn.com.
> mail.china.com.cachecn.com. 191    IN    MX    10 mx-mail-china-com.icoremail.net.
> Thanks.
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