[Mailman-Developers] Camera-ready option to mitigate DMARC issues

[Alessandro Vesely]

On Sat 05/Nov/2016 19:51:13 +0100 Mark Sapiro wrote:
> On 11/05/2016 04:11 AM, Alessandro Vesely wrote:
>>
>> The idea is to add a footer only in case it is not present, similar to
>> what is done with subject_prefix.  By properly setting both of them, a
>> sender can submit what can be called a camera-ready post.  Since no
>> change applies, no DKIM signature breaks.  Hence,
>> dmarc_moderation_action is not needed for such posts.  It is not even
>> necessary to check author's domain policy.
>
> Mailman could conceivably keep track of whether it has changed any
> headers or anything in the body of the post, but it's more complicated
> than that. The first big problem is the Munge From or Wrap Message
> transformations are applied before any msg_header or msg_footer is added
> (or maybe added).

Is it possible to abort processing the in-memory msg and revert to the file? 
Doing so --after thorough checks-- would prevent breaking the signature by 
altering the order of recipient, switching MIME values from token to 
quoted-string or vice-versa, and similar changes that memory representation may 
unwittingly imply.

> I.e. in both MM 2.1 and MM 3, the DMARC mitigations are applied in the
> incoming handler pipeline before the message is queued for delivery
> processing.

All right, so we cannot save that lookup.

> Various decorations such as adding msg_header and msg_footer and modifying
> To: depend on "personalization" and have to be done by delivery processing
> on a per-recipient basis. In fact, the "camera ready" notion can't apply to
> any post that is going to be personalized in any way. This in itself would
> limit the usefulness.

Sure, personalization cannot be compatible with camera-ready.

> It would be more feasible to do this by the poster adding a
> "X-Camera-Ready:" header to the post saying don't transform my message,
> but this is unacceptable as it would bypass content filtering,
> personalization and various other things.

X-Camera-Ready: may be useful to automate at senders'.  For an author doing it 
by hands, having to set a header field is an added difficulty...

>> I'm not familiar with Mailman administration, so I ask your opinion.
>> How long would it take to code this option?
>
> How many angels can dance on the head of a pin?

Ah, not so many of them are still able to perform that, nowadays ;-)

>> Camera-ready posts would be created by hands, by cleverly configuring
>> some email client, or by using purposely written add-ons.  They could
>> also be done by MSAs who care about the damage they cause by publishing
>> p=reject --the process can certainly be standardized and automated.
>
> How does the sender's automated process even know what msg_header and
> msg_footer will be added by the list?

MTAs can learn List-Post addresses when they receive mail.  When they see one, 
they can, say, change the envelope recipient to an internal mailbox which 
processes the decoration (and maybe adds X-Camera-Ready:).  The decorating 
module could be carved out from Mailman, and complemented so as to let it 
download its parameters from well known locations or some such.

Ale