> On 20 Nov 2022, at 21:42, Dave Crocker <[email protected]> wrote: > > On 11/20/2022 1:12 PM, Steve Atkins wrote: >>> On 20 Nov 2022, at 20:48, Dave Crocker <[email protected]> wrote: >>> >>> Remembering that you kicked this off with a heuristic approach, I'm merely >>> noting that a BCC with an addressee listed in it should be just as valid >>> (to the heuristic) as having it occur in To: or CC:. And since you don't >>> agree, I am not at all understanding the basis.
>> It’s a reasonable heuristic if Bcc is included in the DKIM signature, I just >> don’t think including Bcc in the DKIM signature is a good idea. > > Including Bcc: in the signature is a given, for this topic. I've no objection if that’s the given. > > >> Handling of Bcc is not terribly well-defined, particularly for forwarders >> (which will sometimes strip it, and sometimes > > I have no idea what 'handling' you have in mind. To: and CC: do not get > 'handled' except during a Reply process. > > As for 'forwarders', I'm not sure what you mean. Certainly not MTA. That > leaves post-delivery behavior, with re-posting, which is entirely outside the > scope DKIM. Smarthosts rewrite or remove Bcc headers in mail that they accept as a submission from an MUA before they deliver it to the next MTA, in a way that’s implementation (and configuration) defined. Some will do so for mail received from another MTA, not as a submission - e.g. postfix, by default, will strip any Bcc headers after it receives an email and before it passes it to the opendkim milter (I believe, I’ve not tested that.) or forwards it on to the next MTA. One of the ways we’ve tried to make DKIM signing robust across the wild west of the email network has been to avoid signing things that might change in transit. Bcc headers in particular are definitely one of those things, and are special cased as “you should modify or delete this” in quite a lot of places. But perhaps we don’t care in this particular case? If Bcc modification breaks the signature then it’s no worse - for delivery to this single recipient - than it would have been otherwise. I don’t think it affects the broader identification of mail streams for reputation tracking in a way we’d care about either? >> As far as delivery to the recipient is concerned it’s a reasonable argument >> that this only applies to messages where the recipient is not in the To or >> Cc header, so signing the Bcc header is going to be no worse, and may even >> be better in the rare case where the Bcc header includes the 821 recipient, >> and each individual message to each Bcc recipient is signed. > > Sorry I wasn't clear. The premise is that the address in the BCC is a > recipient, listed in an envelope address. Cheers, Steve _______________________________________________ Ietf-dkim mailing list [email protected] https://www.ietf.org/mailman/listinfo/ietf-dkim
