Hi!
On 10/14/26 17:59, Bron Gondwana wrote:
On Wed, Oct 14, 2026, at 11:43, William Weiner wrote:
Hannah,
The concern is not what the spec says. It is what implementations
build from chain depth data once it is available. Spam filters and
reputation systems use available signals regardless of whether a BCP
tells them to. A chain with depth 1 is a different feature value than
a chain with depth n>1, and systems will train on that difference.
The guidance exists so they do not infer more meaning than is
intended. This is to address human factors concern.
A huge chunk of email goes direct. A chain with depth == 1 will be
the common case. I believe (and I think Hannah does too) that you are
chasing a shadow here - there is no substance in this worry.
With the clarification from William, I'm not sure it's _completely_ a
shadow.
Of course any implementation can have a derived variable for each
message that distinguishes _one_ DKIM2-Signature entry from multiple (or
none).
They could then for example try to find if there are correlations
between this variable and spaminess and if so, use that correlation as
one factor in spam/reject/... decisions.
My expectation would be that the correlation would be very low if any.
_Perhaps_ in combination with other traits there could be a little more
correlation (e.g. mail comes from i=1 d=paypal.com _and_ has further
hops _could_ possibly be correlated with somewhat more suspicion).
But, if so, then it could possibly be legitimate to use such signals and
then it's again no problem.
If of course some receiver uses this single feature as criterion without
validating their conclusions, it's like any other mistakes in spam
filtering. (I've seen a spam filter flagging random legitimate mails
from this very mailing-list as clear false positive.)
And I think teaching people how to reduce/get rid of false positives in
spam filtering is way out of scope for a DKIM2 BCP document.
tl;dr: My disagreement is only about saying, one-hop vs. multi-hop isn't
a signal _at all_. Besides that I agree, it's probably a very weak
signal, _and_ the question is probably out of scope for DKIM2 documents.
Hannah.
--
Hannah Stern
Software Developer
Mail Transfer Development
1&1 Mail & Media Development & Technology GmbH | | |
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