On 12/11/22 00:46, Barry Leiba wrote:
2. I send myself email from my account to my account. Of course,
free-email signs it, because it's sent from me to me: why would it
not?
3. I take that signed message and cart it over somewhere else, sending
it out to 10,000,000 recipients through somewhere else's
infrastructure. It's legitimately signed by free-email.com.
Straw-manning a possible mechanism: a DKIM signer is able to include
information about the number of recipients that it intended to take
responsibility for the message to be sent to[1]. A large receiver who's
seeing orders of magnitude more copies knows that something is wrong[2].
Smaller receivers can't do much but probably aren't the major concern. A
privacy concern for email sent by individuals arises because disclosing
that there were any BCCs might be problematic, but this can be resolved
by indicating e.g. "10 or fewer" rather than providing exact numbers,
and the threshold in use can be selected by the signer to best deal with
local conditions.
I have two concerns about the WG proposal:
1. Unless one or more of the larger receivers (a) has a useful tool to
help with this problem, and (b) is willing to share operational
experience, then we risk creating yet another lengthy, academic
exercise (remember ADSP?). I'd suggest that this might be enough
reason by itself not to proceed.
2. How is any possible "break the SMTP/message separation" solution
handled? Does the possibility of doing so need to be expressed
explicitly at this point? Does merely doing so induce additional
bureaucratic hurdles? Does failing to do so tie the WG's hands
behind its back?
- Roland
1: a field in the signature, a message header included in the signed
set, etc.
2: whether the signer was lying or some other party is improperly
amplifying is outside what this mechanism could determine, certainly,
but it seems like a useful datum
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