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

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Autor: Todd Lyons
Fecha:  
A: exim-dev
Asunto: Re: [exim-dev] Bug? Exim rewrites domain in response to CNAME, in contradiction to what is written in Chapter 31
I'm quite happy to acknowledge and accept corrections like this!
Thanks for the info.

...Todd

On Mon, Sep 9, 2013 at 10:04 AM, Viktor Dukhovni
<viktor1dane@???> wrote:
> On Mon, Sep 09, 2013 at 09:00:01AM -0700, Todd Lyons wrote:
>
>> > > nonesuch@www.bcidahofoundation.com
>> > >    <-- nonesuch@???

>>
>> I think it's a terminology issue. It's not exim "rewriting" the email
>> address. I believe a more technically correct phrase would be
>> "normalizing". A domain is not supposed to have an MX record set to a
>> CNAME.
>
> You're mistaken. The illegal configuration is:
>
>         example.com.      IN MX    0 mail.example.com.
>         mail.example.com. IN CNAME smtp.example.com.
>         smtp.example.com. IN A     192.0.2.1

>
> However, the below (which is the OP's situation) is valid (since
> April 2001, RFC 2821):
>
>         example.com.      IN CNAME example.net.
>         example.net.      IN MX 0 smtp.example.net.
>         smtp.example.net. IN A     192.0.2.1

>
> More than a decade ago (prior to RFC 2821), envelope recipient
> addresses of the form localpart@??? (with example.com as
> above) were expected to be canonicalized (normalized if you will)
> to localpart@??? since RFC 821 requires primary names in
> all contexts where domains are used. This was relaxed in RFC 2821
> with the express purpose of allowing <user@???> in
> MAIL FROM: and RCPT TO:.
>
> MTAs are now expected to not automatically canonicalize the domain
> part of envelope recipient addresses based on the presence of a
> DNS CNAME alone. Of course explicit rewriting rules in the MTA
> configuration can rewrite local addresses at will, and remote
> addresses at their peril.
>
>> Behavior when such an event occurs is undefined. Some MTA's
>> merely fix the sending domain from the (invalid) CNAME to the
>> (standards compliant) A record. I *know* sendmail does this as I'm a
>> list owner on a mailing list machine which has this particular
>> configuration. Read on for exim behavior in this scenario:
>
> Sendmail (in best-practice and default configurations) no longer
> automatically canonicalizes the domain part of envelope recipient
> addresses. The same is true of Postfix.
>
>> Yes it has been changed, but no it's not incorrect (IMHO).
>
> Your opinion is contrary to long established standards.
>
> --
>         Viktor.

>
> --
> ## List details at https://lists.exim.org/mailman/listinfo/exim-dev Exim details at http://www.exim.org/ ##




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