On Tue, Aug 25, 2020 at 2:13 PM John R Levine <jo...@taugh.com> wrote:
> On Tue, 25 Aug 2020, Dotzero wrote: > >>> I would expect there to be multiple potential approaches to identifying > >>> acceptable intermediaries. > >> > >> The harder part is to decide which intermediary gets to re-sign which > >> message at the time you apply the weak signature. > > > > It would have be the domain in the "To" field. It wouldn't work with > > random unknown intermediaries. It would address the MLM issue as long as > > the MLM domain is the same as the "To" domain when the message was > > originally sent. It could also presumably work for vanity domains if they > > DKIM sign. It wouldn't work for forwards on the receiver side that the > > sender is unaware of. > > If the list is somel...@lists.foo.org, does the signature have to be > d=lists.foo.org? How about d=foo.org? > This is something that would have to be thought through and discussed. I want to lean towards exact match but I could be convinced that the base organization signature would be acceptable as a starting point. I would recommend anyone coding this for signing to use a flag to easily switch between the two. I'd recommend that any intermediary doing signing consider using the CNAME approach so that all their lists can easily be signed with an exact match signature. This is one of the areas where implementation and operational considerations may differ from standards considerations. > > On the flip side, do you put a weak signature on all of your outgoing > mail, which seems like a bad idea, or just mail that you expect to go > through list modification? In the latter case, how do you tell? These > are the scaling problems that I fear make this unworkable. > I think only putting the weak signature on mail you expect to be modified would be the way to go. As I indicated in my previous post, there are multiple ways to address identifying which mail is likely to go through an intermediary. Large mail providers/data gatherers probably already have an awareness in this space. Others could probably create lists which could be checked realtime or updated/downloaded once or twice a day. Organizations could also enable self registration of intermediary use by their users. It might also be a combination of these approaches. I don't see this as an issue that makes scaling unworkable. There are plenty of folks checking for blocklists, how does this differ significantly either operationally or in scale? Michael Hammer
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