Incoming SMTP in the year 2017 and absence of DKIM

Michael Thomas mike at
Wed Nov 29 17:32:27 UTC 2017

On 11/29/2017 09:24 AM, William Herrin wrote:
> On Wed, Nov 29, 2017 at 12:17 PM, Stephen Frost <sfrost at> wrote:
>> * William Herrin (bill at wrote:
>>> On Wed, Nov 29, 2017 at 12:03 PM, Eric Kuhnke <eric.kuhnke at>
>> wrote:
>>>> How much weight do you put on an incoming message, in terms of adding
>>>> additional score towards a possible value of spam, for total absence of
>>>> DKIM signature?
>>> Zero. DKIM for mailing lists is a horribly broken design and legitimate
>>> mailing lists are second only to spam in quantity of SMTP transactions.
>> Eh, that's really not accurate, imv, and some folks who run mailing
>> lists have put in serious effort to make sure to *not* break DKIM
>> signatures (which is certainly possible to do).
> Alright, so "horribly broken design" overstates the case but there are
> enough problems that weighting the absence of DKIM at something other than
> zero will surely do more harm than good.

There are quite a few things you can do to get the mailing list 
traversal rate > 90%, iirc. For average mailman-like
lists like nanog it's very high. Of course while a "badly" behaving 
mailing list can trivially defeat any DKIM signature,
it doesn't really take too much effort to not behave "badly". Whether 
that false positive rate is too high is another


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