[ietf-dkim] Corner cases and loose ends, was , draft-vesely-dkim-joint-sigs
vesely at tana.it
Mon Sep 27 10:26:37 PDT 2010
On 27/Sep/10 17:07, John R. Levine wrote:
>>> Good point. So it's two things, lists should sign outgoing mail, and
>>> discard any incoming mail with dkim=discardable.
>> No, they should reject the email at SMTP time. The email is NOT
>> discardable when it arrives at the MLM. Rejection at SMTP time does
>> no harm, and gives the sender an opportunity to fix the problem.
+1 for the idea, but...
> OK, so during the SMTP session, more particularly during the interval
> between receiving the dot at the end of data and returning a status
> code, my SMTP daemon needs to:
> * identify recipient addresses that are mailing lists
... that's not quite feasible, since your MLM doesn't have to tell
your MTA what of a particular kind of user it is. So let's say at
SMTP time the MTA accepts the message, possibly flagging it with
dkim-adsp=pass in the A-R field.
Now the MLM does its editing job. It knows the original message was
signed, so it makes sense to verify if the signature is still good
after any changes have been applied. In case verification fails, it
shouldn't try to distribute an adsp-breaking message, so it can either
send back a bounce or drop it.
Going for the bounce is not a bad design decision, because after all
these are signed messages from verified subscribers.
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