As an individual, +1000 to Scott. As Chair, this thread is unproductive, and two months passed due date to resolve. Consensus seems clear that there isn't an issue here. If there's a clear use case that hasn't been communicated, share it now or move on.
Seth On Fri, Feb 12, 2021 at 10:02 AM Scott Kitterman <skl...@kitterman.com> wrote: > I didn't miss it. I don't think it's meaningful. > > In the real world, outside the IETF one of three things happens: > > 1. Everything works fine. > > 2. Someone depends on HELO evaluation of SPF and discovers from > evaluating > the feedback reports that's it's a problem and then doesn't to that > anymore. > > 3. Someone depends on HELO evaluation of SPF and doesn't discover it's a > problem because they don't look at their feedback reports. > > For case 1 and 2, there's no issue. > > Case 3 doesn't care if their mail gets delivered, so its fine. > > This excessive focus on irrelevant minutia is harmful to the IETF. It > makes > participation less interesting for technically capable contributors and > reduces the overall value of the discourse. > > Many people have suggested we move on. My prediction is you won't, but > this > is my last email on the topic. > > Scott K > > On Thursday, February 11, 2021 11:24:16 PM EST Douglas Foster wrote: > > You missed my main point. I will restate it, and then address your > threat > > question. > > > > If there are N ways to establish authentication, then a recipient only > > needs to choose one of them, but a sender who wants to be validated by > all > > recipients must implement all of them. One purpose of the specification > > is to constrain that complexity. > > > > So the convenient solution would be to say that SPF HELO must be ignored, > > except for null sender, because doing so reduces the number of variables > > that must be considered by senders. It is also probably consistent with > > the logic of many current implementations. I just do not believe that > it > > is justified to tell recipients that they MUST NOT evaluate SPF HELO when > > MAILFROM is present. > > > > An alternative would be to say that SPF HELO and SPF MAILFROM should both > > be evaluated. In the long run, this is arguably the best theoretical > > solution, but the fear of short-term pain from false positives probably > > makes this unattractive. > > > > So, I am back to the only solution that seems justifiable: Senders > > SHOULD comply with both MAILFROM and HELO policies because SOME > recipients > > may evaluate both criteria, but many will only evaluate MAILFROM because > > the incremental theoretical benefit seems less than the incremental cost. > > > > - - - > > > > To your point about threat vectors: DMARC alignment is based on nested > > layers of trust, and the trust is broken if you skip layers. The server > > operator provides a mail server environment to a mail domain, and the > mail > > domain provides delivery services for an author. > > > > SPF proves that the mail domain (indicated by the MAILFROM address) > really > > uses the services of the server domain, and therefore the server > (indicated > > by IP address, HELO, and possibly ReverseDNS) is authorized to send > > messages on behalf of the mail domain. > > > > DMARC proves that the source server for the message was authorized to > speak > > on behalf of the author (indicated by the From address). > > > > You suggest that if SPF HELO passes, and aligns with FROM, then we have > > established that the server is authorized to speak for the author. This > > is true, but it does not establish that the mail domain in the MAILFROM > > address has that right. > > > > When the MAILFROM domain is different from the HELO domain, this implies > > that that MAILFROM domain is a client of the server domain. The server > > domain has the right to emit messages for the client, but the client > domain > > does not have the right to email messages claiming to be from the server > > domain. > > > > - - - > > > > It can be asserted that the server domain should be able to use its > > firewall to prevent unauthorized servers from emitting mail, and should > be > > able to use its outbound gateway to prevent client domains from emitting > > messages from the server domain, other clients, or any unrelated domain. > > These commonly implemented measures could eliminate the need for checking > > SPF HELO. Why should others check what the sender should be able to do > > for themselves? > > Are we prepared to make this argument? If so, then the existing wording > > stands, but needs a solid justification. > > > > DF > > > > On Thu, Feb 11, 2021 at 8:50 AM Scott Kitterman <skl...@kitterman.com> > > > > wrote: > > > What problem are you purporting to solve? > > > > > > By problem, I mean a case were a bad actor can get a DMARC pass result > if > > > SPF > > > HELO results are allowed to be used that they couldn't already get > with a > > > mail > > > from result. > > > > > > I don't think such a case exists which is why I think this entire line > of > > > argument is a waste of time. > > > > > > Scott K > > > > > > On Thursday, February 11, 2021 6:35:49 AM EST Douglas Foster wrote: > > > > Applying SPF to DMARC could become out of scope, if we choose to > remove > > > > > > SPF > > > > > > > from DMARC and make it dependent only on DKIM. Until then, we need > to > > > > have a shared understanding of how SPF is applied. This question > asks > > > > whether that shared understanding exists. > > > > > > > > SPF involves two tests, which can be used together. This WG can > insist > > > > > > > > that for DMARC purposes, only one can be used: > > > > "When the sender is not null, DMARC-evaluation only considers the > > > > SPF > > > > > > > > evaluation of the MAILFROM Address. SPF evaluation of HELO MUST > NOT be > > > > considered for DMARC purposes." > > > > > > > > This wording seems implied by the current language, and by those who > > > > want > > > > to leave it untouched. Implication is different from specification, > so > > > > > > our > > > > > > > document should make this explicit. Unfortunately, an explicit MUST > > > > NOT > > > > requirement is hard to justify. When two domains are involved, and > > > > both > > > > domains have published policy information, what justification exists > for > > > > ignoring some of the available security-related information? > > > > > > > > If we back away from MUST NOT, then we have to consider that some > > > > recipients MAY evaluate SPF HELO and SPF MAILFROM together, just as > the > > > > > > SPF > > > > > > > RFC expected them to be used, and as outlined in one of my examples. > > > > > > If > > > > > > > some recipients MAY evaluate HELO, then senders SHOULD take care to > > > > > > ensure > > > > > > > that HELO will generate a PASS. Our language becomes something like > > > > > > this: > > > > "When the sender is not null, DMARC-evaluation always uses the > SPF > > > > > > > > evaluation of the MAILFROM Address. Some recipients may evaluate > SPF > > > > > > HELO > > > > > > > as well. To maximize recipient trust, senders SHOULD publish an SPF > > > > policy which ensures that both MAILFROM and HELO will produce SPF > PASS > > > > results." > > > > > > > > DF > > > > > > > > On Wed, Feb 10, 2021 at 6:29 PM Dave Crocker <dcroc...@gmail.com> > wrote: > > > > > On 2/10/2021 3:24 PM, Douglas Foster wrote: > > > > > > Huh? Are you asserting that SPF MAILFROM and SPF HELO are > > > > > > interchangeable? They are not, but they can work together. > > > > > > > > > > Perhaps I misread, but I thought I saw that this really is out of > > > > > scope > > > > > for this working group. > > > > > > > > > > > > > > > d/ > > > > > > > > > > -- > > > > > Dave Crocker > > > > > dcroc...@gmail.com > > > > > 408.329.0791 > > > > > > > > > > Volunteer, Silicon Valley Chapter > > > > > American Red Cross > > > > > dave.crock...@redcross.org > > > > > > _______________________________________________ > > > dmarc mailing list > > > dmarc@ietf.org > > > https://www.ietf.org/mailman/listinfo/dmarc > > > > > _______________________________________________ > dmarc mailing list > dmarc@ietf.org > https://www.ietf.org/mailman/listinfo/dmarc > -- *Seth Blank* | VP, Standards and New Technologies *e:* s...@valimail.com *p:* 415.273.8818 ` This email and all data transmitted with it contains confidential and/or proprietary information intended solely for the use of individual(s) authorized to receive it. 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