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Re: Spamassassin and the like

2003-06-25 11:44:20
At 08:48 2003-06-25 -0400, Hal Burgiss wrote:
How much spam do you get, and what is an acceptable failure rate for
you? Just curious. I cannot see an MTA approach being more than 80-85%
effective,

That's 80-85% less junk messages that you have to sort through - and the legit senders receive a bounce, whereas post-SMTP filtering generally (and SHOULD) involve filing it away, often in trash - the occasional legit sender never knows that their message was classified as junk, so they assume you're ignoring them.

If you block spam at the SMTP level - based on sender domain (access.db) or originating IP (DNSBL), BEFORE the spam has been received, then you don't suffer a significant network bandwidth hit - a few lines of transaction (EHLO, RCPT TO, and associated acknowledgements), and you're done. In fact, when the bounce message is generated and sent to the message originator, it's the _sending_ host which actually sends that message - your mail host simply provided the one-line reason the message was rejected.

In my case, I create DNSBL error messages which contain clickable URLs, inclusive of the blocked IP address, and an DNSBL-specific anchor which hit a policy page on my own site. Legit users who receive a bounce can simply click on the URL in the message and be directed to a page which explains why, and in turn provides a link to the DB lookup for the specific DNSBL.

I use SMTP blocks, and *then* still filter using my own procmail rules. No SA here, though I don't doubt that it is a fine product (actually, it is used at a small ISP which I do admin work for, and has proven quite effective - I've even set up procmail rules for a friend to dump the messages which are above a certain SA threshold, so he doesn't have to download them, and there's a crontab which cycles the spam mailbox weekly (spam -> spam.old), so he has some time to recover anything which may have been misfiled, but otherwise doesn't have to do anything to keep from amassing a large spam mailbox).

---
 Sean B. Straw / Professional Software Engineering

 Procmail disclaimer: <http://www.professional.org/procmail/disclaimer.html>
 Please DO NOT carbon me on list replies.  I'll get my copy from the list.


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