[ietf-dkim] authentication result headers are an unsafe alternative

[Douglas Otis]

On Apr 18, 2006, at 10:42 AM, Scott Kitterman wrote:
>
> From a protocol design perspective, I think the right answer is to  
> design for the case where the receiving MTA/MDA will check the  
> signature and record a result that, if appropriate, an MUA can use.

Depending upon an unsigned "results" header being added to the  
message is an unsafe practice.

It is not practical to determine who added the "results" header,  
whether the MDA strips/adds all prior results headers, and whether  
all possible backup and alternative paths also strip/adds all  
"results" headers.  Retaining the integrity of the DKIM signature for  
a suitable period should permit message verification for transports  
that carry messages beyond the MDA.  Message protection beyond SMTP  
is an important aspect of DKIM.  Reliance upon a results header may  
produce many years of victims that DKIM intended to protect.

Explain the motivation for not including DKIM protection beyond SMTP?

-Doug