[dns-operations] MX CNAMEs

[Mark Andrews]

In message <45fb5af36ca944258e05c493da5a7fcb at DFM-DB3MBX15-07.exchange.corp.microsoft.com>, Jason
 Sherron writes:
> CloudFlare's take on the related CNAME issue with an explicit calling-out 
> of MS Exchange for MX records
> 
> http://blog.cloudflare.com/introducing-cname-flattening-rfc-compliant-cnam
> es-at-a-domains-root/
> 
> (Yes, I work for MSFT but have no opinion or knowledge of the specifics 
> here. I just liked the article.)

Which is unrelated to the use CNAME of as MX/SRV targets.
 
> -----Original Message-----
> From: dns-operations mailto:dns-operations-bounces at dns-oarc.net On Behalf 
> Of Mark Andrews
> Sent: Thursday, December 25, 2014 11:39 PM
> To: 
> Cc: dns-operations at dns-oarc.net
> Subject: Re: dns-operations MX CNAMEs
> 
> 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,  <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    202.108.3.242
> > 
> > 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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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org