On 5/7/2010 10:07 AM, John R. Levine wrote:
No, all it says is "we signed this mail." A signer with a good reputation
will presumably rarely sign mail where the From: address actively
misidentifies the sender, but that's a second order effect.
"misidentifies" covers quite a lot.
I used it to mean that the From: address doesn't have a reasonable
connection to any of the persons or entities that composed the message,
for some reasonable definition of reasonable.
If I send mail from bbiw.net (well, actually, sbh17.songbird.com is my
standard MSA) but label the From: field as being gmail.com, that's reasonable
to classify as "misidentifying" the From: address, since songbird has nothing
to do with gmail.
No, that's not misidentification. It may be something else, but we need
more precise terminology, preferably that avoids loaded terms like
"forgery".
Operator-based signing is typically meaning that the message was posted by an
authorized user. There's absolutely no implication that the operator checked
or enforced the contents of the From: field.
That entirely depends on what you know about the signer. Two of the
largest signers, Google and Yahoo, mechanically check that the user
receives mail at the From: address. One of the smallest, me, knows his
users well enough to be confident that they won't do hostile address
fakery even though I don't enforce anything mechanically beyond adding
trace headers. I have other opinions about other signers.
I'm realizing that a basic problem we have with explaining DKIM is that it
makes semantic rather than operational assertions about messages. Since we
are nerds, many of us deeply want to assign operational definitions, like
"the people who know the passwords to the MTA that emitted this mail also
know the passwords to the DNS server for the domain in the From: line",
but they don't work, particularly for list mail in which the only
operational definition of a good list is one where the recipients like
what it sends.
So here's a scenario. Let's say I run a political satire mailing list, to
which members contribute wacky messages pretending to be from famous
people like billg(_at_)microsoft(_dot_)com or sarko(_at_)elysee(_dot_)fr(_dot_)
I use some technique
not visible in the outgoing mail to ensure that the contributions are from
list members (perhaps a password that's stripped out.) Of course the list
puts a shiny new DKIM signature on all its mail. The list is triple
opt-in with a cherry on top, and the subscribers await each list message
all agog. Filter that.
R's,
John
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