On Mon, 7 Jul 2008, Jeroen van Aart wrote:
Andrew Daviel wrote:
We run procmail rules for server-side spam filtering, using dmail as the
delivery agent for MIX format. Generally this works well.
Wouldn't spam filtering at the smtp level be more effective and cause less
traffic? It's important to be able to reject a message asap, preferably
before any data goes through (grey listing, rejecting certain IP-addresses,
etc.). So you have the least possible waste of resources.
Yes, we do that too - RBL at RCPT time plus spamassassin milter at DATA
time. Currently it looks like 80% is rejected at RCPT, 10% at DATA, and
3% filtered on delivery, leaving 7% legitimate mail. The RBL
rejected number seems on a linear rise over the last year :-(
Mail scored over one threshold is deemed "definitely spam" and rejected
by SMTP DATA response.
Mail scored over a lower threshold is deemed "possible spam" and
accepted, allowing users to filter it, adjust whitelists etc.
They can also have multiple inboxes for mailing lists etc. if they wish.
Mail scored below the low threshold is deemed "ham" (sic).
One problem with filtering up front is that messages must be scored
before they are cloned, meaning that a user's personal whitelist cannot
be applied if there is more than one recipient. Just in case we have some
spam-lovers, or commercial newsletters that trip the threshold...
--
Andrew Daviel, TRIUMF, Canada
Tel. +1 (604) 222-7376 (Pacific Time)
Network Security Manager
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