spam removal

matthew matthew at
Mon Feb 16 02:57:42 PST 2004

On Mon, 16 Feb 2004, Paul A. Hoadley wrote:

> On Mon, Feb 16, 2004 at 04:44:25AM -0500, matthew wrote:
> > > I recommend bogofilter for per-user filtering.  Spamassassin is
> > > also highly recommended for site use.  I tend to dislike DNS-based
> > > filtering because it has a high rate of false positives, and it
> > > causes your users to lose legitimate mail if it's rejected at the
> > > mail server.
> >
> > As far as I understand it, one does "not lose email" using dns-based
> > blacklists.
> Sure you can.  If Alice wants to legitimately contact Bob from a
> blacklisted IP (whether the blacklisting is actually Alice's fault, or
> she's just fallen under an excessively large blanket), and Bob is
> running DNS-based filtering, Bob's MTA blocks Alice based on her IP.
> Bob loses legitimate mail.

We have different opinions on what it means to lose email.
An email is lost when no error message is returned to the sender
and the email never gets to its intended recipient.

Your example, if you play it out further, Alice will be well aware
her message did not get delivered. She sent that email from a real
mta. That mta records the error mesg Bob's dns-blacklist using email
server spit out. You know what i mean, same thing goes with a user

So Alice knows the email was not lost. She is now aware of why,
hence the http://url in the error mesg. And now Alice can contact
her admin, and figure out why that ip/block is spewing spam
at me/us/blacklist users.

So in summary, dns blacklists do not "lose" email.
The email was never sent by Alice's email server
and she is aware why.


> Admittedly you provided a counterexample,
> but it is not always so easy.
> --
> Paul.
> mailto:paulh at
> mailto:phoadley at
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