28 May
2015
28 May
'15
5:11 p.m.
On 2015-05-28 23:06, Antonio Querubin wrote:
(Please trim inclusions from previous messages)
_______________________________________________
On Thu, 28 May 2015, Rob Janssen wrote:
And to add to the that. MX -> CNAME is 'allowed' in DNS, it will just
break as Sendmail for instance will then rewrite the To: address.
Eg in the above example it will rewrite mail to @name to some.mail.server.
And that is why you don't want to do CNAMEs with MXs.
Or as described at https://www.sixxs.net/faq/account/?faq=email :
8<-----
Using a CNAME in your domain breaks your email because sendmail (and
possibly other SMTP software) will rewrite the domain portion of the
destination email address to that of the label in the CNAME. See also
CNAME records in mail by D. J. Bernstein[1]. Note that having a CNAME
for example.tld is of course impossible unless you get the tld to have
the same record. Having an MX point to a CNAME record causes additional
DNS lookups, which might cross a threshold, and thus cause your mail to
be dropped. Additionally "Mail loops back to me" errors might be caused
by this. Also see RFC1034[2] - DOMAIN NAMES - CONCEPTS AND FACILITIES
for more details. In short: Don't use CNAMEs in relation to SMTP.
[1] http://cr.yp.to/im/cname.html
[2] http://www.ietf.org/rfc/rfc1034.txt
----->8
See also https://www.ietf.org/rfc/rfc1912.txt for common mistakes.
Greets,
Jeroen
But that is not what I mean. What is NOT
allowed (by the spec) is to
have:
name IN MX 10 mail
mail IN CNAME some.mail.server
So you can have a CNAME pointing to MX, but not MX pointing to CNAME.
To be specific, a CNAME RR points to another name which could be an MX
RR. Apart from associated DNSSEC RRs, a CNAME basically overrides
anything else defined for that name.