pre-download filtering (was Re: Spamassassin not doing blacklist lookups)
On Wed, Nov 16, 2005 at 07:58:07PM +0000, Adam Hardy wrote:
> sorry if this is a dumb question, but your email implies spam-assassin
> does DNS look-ups to filter out spam - which is not what I thought
> after giving spam assassin the once-over check-out. Is it so? What
> level of effectiveness does it have?
>
> And can it actually filter your pop3 server's inbox before download?
Not sure about spamassassin in general, but most static rule-based
filters have some rules which are applied to the headers, and some which
are applied to the body. Presumably, in order for there to be an
advantage in filtering before download, you don't want the entire
message fetched and scanned locally, so the filter must be operating on
either just the headers, or a preset number of lines of body too[1].
So, the accuracy of such a filter would be entirely limited to those
rules which were applicable to the headers only, say[2]. Is that really
good enough?
[1] I believe it would have to be a line-based cut-off, due to POP3
protocol restrictions.
[2] These include many of the rules mentioned in this thread
(RECV_IN_SOMERBL, SUBJECT_VIAGRA or whatever)
--
Jon Dowland
http://jon.dowland.name/
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