Re: [dmarc-ietf] DMARC alignment conflicts with RFC 5322 on the use of the From and Sender header fields

[Pete Resnick <[e-mail]>]

On 2 Jun 2020, at 13:29, Dave Crocker wrote:

> On 6/2/2020 11:12 AM, Pete Resnick wrote:
>> On 2 Jun 2020, at 13:01, Dave Crocker wrote:
>>
>>>> There's no reason that DMARC couldn't have included the sender or 
>>>> tried to have some kind of
>>>> PRA like spf v2... but that's not the goal.
>>>
>>>
>>> But the Sender: field is not reliably present and, of course, DMARC 
>>> needs an identifier that is reliably present.
>>
>> Dave, could you explain that? Coding-wise, there's surely no reason 
>> that an implementation can't say, "if 5322.sender is present then 
>> sender = 5322.sender else sender = 5322.from". So you could say that 
>> the identifier of sender is reliably present, since it's taken from 
>> 5322.from if 5322.sender isn't present. But maybe I'm missing 
>> something. Please explain.
>>
>
> Not sure what you are asking.  What I mean is that it isn't always 
> present.
>
> If Sender: contains the same address as From:, then Sender does not 
> have to be present, and often/usually isn't.

Well, that's the field, not its value.

> So when someone comes along and changes From: -- such as to hack 
> around the DMARC problem for intermediaries -- the semantic of the 
> Sender information is lost.

If you do change the From, you should always add a Sender. (Or is your 
point that implementer's don't, and that's the problem?)

What I'm missing is why the lack of an actual Sender: header field is 
problematic.

pr
-- 
Pete Resnick https://www.episteme.net/
All connections to the world are tenuous at best