Re: [exim-dev] Bug? Exim rewrites domain in response to CNAM…

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Autor: Max Bowsher
Data:  
Dla: Graeme Fowler
CC: exim-dev@exim.org
Temat: Re: [exim-dev] Bug? Exim rewrites domain in response to CNAME, in contradiction to what is written in Chapter 31
On 09/09/13 14:36, Graeme Fowler wrote:
>
> graeme@boom ~]$ dig bcidahofoundation.org any
>

[...]
>
> ;; ANSWER SECTION:
> bcidahofoundation.org.    900    IN    CNAME    www.bcidahofoundation.com.
> bcidahofoundation.org.    85677    IN    NS    ns1.hover.com.
> bcidahofoundation.org.    85677    IN    NS    ns2.hover.com.

>

[...]
>
> ***Interesting bit here*** bcidahofoundation.org has no MX records,
> having only a CNAME at the zone apex which goes to... ta-da! The
> explicit hostname of www.bcidahofoundation.com.
>
> So nonesuch@??? gets internally rewritten in the
> envelope to deliver to nonesuch@www.bcidahofoundation.com.
>


Hi Graeme,

I've snipped much of your message to focus in on one particular part of
it in this reply, specifically the explanation you gave above.


1) Why should a CNAME cause the envelope to be rewritten at all?


2) This behaviour exactly contradicts the third paragraph in the Exim
documentation at
http://www.exim.org/exim-html-current/doc/html/spec_html/ch-address_rewriting.html


3) If I do a "mx" query rather than an "any" query, dig shows another
interesting detail:

;; ANSWER SECTION:
bcidahofoundation.org.    892    IN    CNAME    www.bcidahofoundation.com.
www.bcidahofoundation.com. 79792 IN    CNAME    bcidahofoundation.com.
bcidahofoundation.com.    600    IN    MX    10 mail2.bcidaho.com.
bcidahofoundation.com.    600    IN    MX    10 mail1.bcidaho.com.


Critically, there is a *chain* of CNAMEs:

bcidahofoundation.org
--> www.bcidahofoundation.com
--> bcidahofoundation.com

It does not seem to make much sense for Exim to rewrite to an
intermediate point in the chain - yet that is what it does.


All taken together, it seems fairly conclusive to me that this is
unintended behaviour.


Regards,
Max.