Re: [ietf-smtp] EHLO domain validation requirement in RFC 5321

[Keith Moore <[e-mail]>]

On 9/27/20 11:40 AM, John R Levine wrote:

>> I would say instead that because some subset of inbound MTAs do EHLO 
>> verification, "real mail servers" (i.e. those which manage to 
>> continue to deliver mail with some reliability) are forced to have 
>> static IPv4 source addresses for which PTR lookup results match EHLO 
>> arguments.
>
> No, we've observed in practice that hosts that don't have matching 
> PTRs are spambots.

I don't believe that anyone takes enough time to look at a sufficient 
volume of email, often enough, to be sure of that. And again, it's a 
self-fulfilling belief.

>
>>> Anything that comes from a dynamic or NAT pool is invariably spam 
>>> from a botnet.
>>
>> No, because nobody is looking that closely.
>
> Sorry, but you're just wrong.  We absolutely look that closely.  I 
> know people who maintain pools of patterns to recognize dynamic pool 
> rDNS which lots of people use in their spam scoring.

I didn't say it wasn't used, I said it wasn't reliably measured.

>
> It would be nice if mail still worked the way it did 30 years ago, but 
> that was most definitely then, and this is now.
>
And poorly chosen spam filters are a big reason for the degradation of 
email reliability during that time.

Keith