Another approach that works really well for us:

We send all spam to a gmail account. Then every week we look to see
what google proclaims to be ham and forward it to our clients.

Our numbers tend to break down as follows:
10% Ham & sent to client
1% SPAM & sent to client
8.5% SPAM sent to gmail for processing
..4% SPAM sent to gmail, G says it's ham, but it's spam
..1% SPAM sent to gmail, G says it's ham, we forward it to the cllient.

John
On 7/10/07, John D. Hardin wrote:
> On Tue, 10 Jul 2007, Skip Brott wrote:
>
> > My procmail script is set up to junk all emails with a score over
> > 10.0 and other "low spammy" emails are directed to a generic
> > corporate spam email account for review.

>
> Mine does per-user spam quarantine folders. Feel free to customize it
> to fit your needs.
>
> http://www.impsec.org/~jhardin/antispam/
>
> --
> John Hardin KA7OHZ http://www.impsec.org/~jhardin/
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