North American Network Operators Group

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Re: Misguided SPAM Filtering techniques

  • From: Tony Finch
  • Date: Mon Oct 22 14:50:35 2007

On Sun, 21 Oct 2007, Nathan Ward wrote:
>
> http://www.ietf.org/rfc/rfc2476.txt

Note that this has been superseded by RFC 4409. More recommendations about
the operational and policy issues are laid out in
http://www.ietf.org/internet-drafts/draft-hutzler-spamops-08.txt which
will soon be published as RFC 5068. Sadly it doesn't say much about the
rationale for its recommendations, especially why it's not OK to block 587
even when it might be OK to block 25, because talk of port blocks rapidly
descends into flame wars. However it's fairly clear if you think about who
suffers from spam sent via port 587.

The key point is that the operators of an MSA has a strong incentive to
keep their users clean, or at least their mail flows clean, because any
spam sent via their MSA will (typically) go out of the same relays whether
the client is on site or roaming or using the webmail service. Therefore
reputation problems (AOL spam complaints, blacklistings, etc.) will accrue
where it hurts. The situation is very different for port 25 email, becase
the target MTA has no control over the senders. Access providers don't
care about their access networks having bad spam reputations because the
pain doesn't affect them directly enough.

Tony.
-- 
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