Subject: RE: [Asrg] 7. Best Practices - DNSBLs - Article

From: Jason Steiner <[email-masked]>
Date: Thu, 14 Aug 2003 09:15:06 -0700

"Yakov Shafranovich" <[email-masked]>
> 
> I am not suggesting that a consent system should use ALL available 
> sources, just more then one. Two DNSRBLs or a DNSRBL combined 
> with a filter might be better than relying on SPEWS.org or some other 
> DNSRBL as a sole source of information. Decisions on spam should 
> not be based on a single source alone.

Why? If that single source is reliable and does a good job of implementing
the policies I choose for my mail servers (eg. "We don't want mail from 
dialups here.") , what is the point of incurring the extra load of querying 
more than one, especially if the second is going to be much more resource 
intensive? (eg. A content filter behind a DNSBL.)

jason

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From: "Chris Lewis" <[email-masked]>
Date: Thu, 14 Aug 2003 12:36:35 -0400

> intensive? (eg. A content filter behind a DNSBL.)

Indeed.  Spam filtering is all about systems making informed choices for 
their own needs.  If system A thinks that a randomly generated "block 
this" choice fits  their needs, and system B thinks that 75 different 
filters have to be unanimous before blocking, who are _we_ to judge 
which is better?  Not our machine.  Not our users.  None of our business.

Instead, we should be focusing on:

a) making sure that systems _can_ make informed choices by ensuring that 
filtering methods tell the truth in a simple way of what they do
b) making suggestions on operational "properties" (such as consistency 
to published standards, delisting mechanisms where appropriate) rather 
than the blocking criteria themselves.

There is a DNSBL that blocks all of IPv4 space.  There is another that 
returns a randomly selected block/non-block indication on every query. 
Are they bad/non-BCPish?  No, because they're perfectly clear and honest 
about what they do (including a comment about how dumb it would be to 
actually _use_ them to filter email ;-).