Re: [EAI] Re: SPF and DKIM

[John C Klensin <klensin at jck.com>]

--On Friday, 09 March, 2007 08:44 +0100 Harald Alvestrand
<harald at alvestrand.no> wrote:

>> Yes, but users/clients dont know whether their provider has
>> SPF record in their ALT-ADDRESS,
>> If there are SPF in thoes domain include '-all' , that maybe
>> cause their mail to be rejected.
>> Mail adminstrator is hard to explains those issue to their
>> clients.
>>   
> I think the brutal answer is "don't do that".
> If you use an email address in an ALT-ADDRESS, that needs to
> be an email address controlled and managed by someone who's
> actively supporting UTF8SMTP - including mangling the SPF
> records (if any) to allow the gateways to send the messages as
> needed.

I may be wrong, but I think that, in the overwhelming number of
cases in which downgrade is actually plausible, Abel's analysis
is going to turn out to be equivalent to "for a
backward-pointing address, either 

(1) Use SPF without ALT-ADDRESS, thereby guaranteeing message
rejection if a downgrade situation arises.

(2) Use ALT-ADDRESS without SPF, thereby losing whatever
benefits SPF is expected to convey but without the risk of an
apparently-clear SPF rejection.

(3) Use them together and just hope that, if downgrading occurs,
it occurs with a domain context that is sufficiently permissive.

And, again, if someone wants to put that, or other comments,
into a separate document that is not on the WG's plate (or
discussed on its mailing list), at least in the near term, I
think that would be great.  In particular it is a set of issues
that such a document might usefully bring to the attention of
the SPF community.

     john


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