Re: greylisting done at end of headers, or end of daya (QUIT) ?

Valdis(_dot_)Kletnieks(_at_)vt(_dot_)edu wrote:
> I stopped having sympathy for non-compliant good guys quite some time ago.
> There's no excuse for it in this day and age, especially for the examples
> you give.
>   
The examples I gave were relevant only to the topic at hand: the costs 
of gray listing. It's a pretty small cost, and a cost I was happy to 
accept for three years, since it was stopping spam. It's not stopping 
any spam for me any more, so now the cost -- even though it was quite 
low -- has become too high.
As far as the more general problem of  Good Guys doing bad things, I 
could spend all day on that; it's what I did for a living for the past 
2+ years. Here's as brief as I can get:
There are a small number of compliance checks that work pretty well for 
almost anyone and have low cost. My favorites include accepting mail 
only at MX hosts, rejecting mail whose bounce address doesn't resolve, 
and rejecting mail from IP addresses that don't have a PTR. Nearly all 
of the Tier 1 ISPs do the same.
There's a much larger set of compliance checks that only work for 
specific user communities. Within those communities they work well, you 
can measure it. Within other communities they'll mostly just give you 
false positives. The trick is figuring out which ones do work, and then 
monitoring them, because what worked yesterday might now work tomorrow.
Specific example: I did some research on the accuracy of several 
anti-spam tools that perform volume sampling, comparing the results with 
known volumes. In the case of DCC -- a tool I used fondly for many years 
-- I noticed that I wasn't actually measuring overall Internet E-mail 
volume; I was sampling the nature of the E-mail lists to which DCC users 
subscribe. I found, for example, that DCC users like surveys and geekish 
mailing lists. But they don't subscribe to sex lists or sweepstakes, and 
they don't buy much stuff online from general merchandisers. It was 
pretty spooky, actually, data that a targeted marking guy would have loved.
The survey folks, the geek lists, and the sex sites send the squeeky 
cleanest most compliant mail you will ever find anywhere. (In the case 
of the sex sites, they have to: they've got the "bicycle shop in China" 
problem big time.) But sweepstakes and online general merchandiser's 
compliance is terrible. A filter that relied heavily on standards 
compliance would work very well for the DCC community. But for another 
community that likes sweepstakes and buys lots of stuff online, that 
filter is going to run into a load of false positives.
<csg>