North American Network Operators Group

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Re: Anti-spam System Idea

  • From: Sean Donelan
  • Date: Sun Feb 15 19:21:54 2004

On Sun, 15 Feb 2004, Jon R. Kibler wrote:
> > DialUp Lists (DUL) dns block lists permits you to ignore e-mail from
> > many dynamic IP addresses. You can configure your mail server to do this
> > today without waiting for ISPs to do anything.
> >
> > Like most other "simple" solutions, how effective is it?
> We block known dialup netblks. Catches < 5% of spam. Why? Because the real
> culprits are xDSL, CABLE and other systems with broadband connections. These
> account for about 80% of the spam attempts we observe.

Why don't you block "known" dynamic netblks, including xDSL, Cable, and
other broadband connections using dynamic addresses such as WiFi in
Starbucks?  Most of the existing public DUL's include dynamic IP addresses
from all network technologies, not just dialup.

> The idea here is not just to prevent the receipt of spam (which is what
> DNSBLs can accomplish), rather, it is to prevent the generation of spam
> that is accounting for such a growing amount of everyone's network traffic.

All mail traffic (legitimate and illegitimate) is a very small percentage
of network traffic.  Besides, connections blocked at receipt use a very
small amount of bandwidth.  When the ISP blocks the traffic, you loose the
capability to make an exception when you decide.

> If you block the ability of non-legitimate MTAs (such as open proxies and
> spamiruses) to send spam, you reduce the network bandwidth waste that spam
> is consuming. (As a side effect, you would also reduce the spread of viruses
> by email.)

Blocking port 25 blocks the ability of all MTA's to send any type of mail.
"Non-legitimate" is a determination best made by the two parties involved
in the communication.