On Dec 20, 2007, at 10:44 AM, Michael Thomas wrote:
That would be a bad idea. I believe they changed this in the most
current version, but gnu mailman -- as an example -- was stripping
out DKIM signatures thinking they were doing the originating domain
a favor since they "knew" that the signature would fail (which, in
fact, wasn't always the case). It took quite a bit of convincing on
my part that they should just leave it alone. It's not hard to
understand their perspective though: they thought a broken signature
would look more spammy than a missing signature. Rinse, repeat.
A mailing-list not breaking signatures is a scary idea. This would
open the door for all sorts of abuse.
When a mailing-list signs using DKIM, while not modifying the From
header, they should also expect verifiers to evaluate the From header
signature first. Depending upon the available resources, a second
evaluation of the mail-list signature may not occur. The _only_ way a
mailing-list could ensure their signature is evaluated is to remove
broken From signatures. Leaving these broken signatures needlessly
wastes resources and looks spammy. From what you just suggested about
not breaking signatures, their user's very messages might well be used
to carry spam.
-Doug
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