Re: DKIM and DMARC, Email explained from first principles

Sam Varshavchik <[email protected]> Tue, 25 May 2021 22:11:54 -0400
Newsgroups	gmane.ietf.smtp
Message-ID	<[email protected]>
Dave Crocker writes:

> Actually, no, that's not what I said.  Bad actors are always the first to  
> adopt the newest anti-spam technologies, to abuse those unfortunates who  
> interpret DKIM the way you described.
>
> DKIM establishes a clean (noise-free) channel from the signer, which means  
> that any assessment about them really is about them.  If they are bad  
> actors, that is a lot easier to assess, as is if they are good actors.

Ah, but the first paragraph's the rub. That's why I saw DKIM-Signature: as a  
spam indicator: the bad actors' initial take-up of DKIM-Signature: was quite  
noticable.

That was definitely true at one point. Based on today's numbers that I  
looked at the mainstream adoption of DKIM sadly diluted its early value as a  
spam indicator, ironically.


>> But nearly all other spam, the kind that I do have a major problem with, the  
>> specific type that I'm bitching about, nearly all of it carries a DKIM- 
>> Siganture: field. I only found very, very few exceptions to that.
>
> For those assessed as bad actors, was any of their mail mixed in with mail  
> from a different signer who was assessed to be a good actor?

My sample wasn't large enough for that. I have no recollection of seeing  
this; except I have a dim recollection of receiving something non-spam from  
Sendgrid a very, very long time ago, before I wrote them off as damaged  
goods.

Interestingly enough, while researching this response, I found a copy of a  
sendgrid-sourced spam from December 2020, from a previously unknown (to me)  
IP address range (it was spamming an SMS-spam service). It did not have a  
DKIM/DMARC signature of any kind. Nothing from Sendgrid since then until  
today, when Sendgrid attempted to spam one of my Sourceforge mailing lists,  
with a monstrous DKIM-signed spam in Spanish.

So, looks like Sedngrid is
>> Now, to John's point, that DKIM alone is not indicative of reputation, that  
>> it only serves to ascertain identity, and with that out of the way you can  
>> now evaluate the proven identity's reputation. Well, the problem with that  
>> is twofold:
>>
>> 1) There are no known (at least to me) established reputation providers. And  
>> even if there are some that claim to be, history teaches that they don't  
>> really accomplish much.
>
> Gosh, you mean that each evaluator needs to formulate their own criteria,  
> about a complex, fuzzy topic?  Yup!
>
>>
>> 2) So you're left with building and maintaining your own reputation database.
>>
>> That seems like a lot of work to me.
>
> It is.  Sad reality.  Lot of criminals on the streets make safe navigation  
> challenging.  Most people need to outsource their safety efforts.

You can't really have both. Either you "formulate your own criteria", or  
you'll outsource your spam filtering.

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