Re: [dmarc-ietf] Signaling MLMs

[Barry Leiba <[e-mail]>]

> I've also been thinking about ways to push the burden back on the
> advertisers.  Imagine we have some kind of signaling mechanism that
> MLMs can take advantage of indicating to them that the author is using
> a strong policy, and so it would be possibly a bad idea for the MLM to
> accept, mutate, and re-send this message.  This could be a header
> field or an SMTP extension (though the latter is complex to get right
> in a store-and-forward system).  The MLM can then decide if it is
> willing to pass the message unmodified to the list, or reject it with
> an error like "The policies of this list require modification of your
> message, which violates your domain's apparent policy.  Your
> submission therefore cannot be accepted.  Please contact your support
> organization for further assistance."  There's never an opportunity
> for the collateral bounce to occur if the message is never
> distributed, and the author domain has to either soften its policy or
> separate its regular users from its transactional stuff somehow.

There's no need for a signal here: the MLM can simply check the
sending domain's DMARC policy when a new post comes in, and
preemptively reject it if the policy is "reject".  The IETF considered
doing that and ruled it out because it would mean that users with
yahoo.com addresses (and others) could then not participate in IETF
mailing lists without changing addresses.  I think that was the wrong
decision, but we decided on the ugly "from" alteration instead.

I still think that outright refusal of posts from p=reject domains is
a good approach and I wish it were used more, but most MLMs that are
willing to put in a change to address this seems to prefer not to
punish the sending domains users for the excesses of the domain
management.

Barry