At 15:43 2005-06-30 -0400, Chris Payne wrote:
Thanks for the reply Sean. I was doing some digging after my posting to
the list, and found "virbl.bit.nl".
I currently use spambouncer to address the many BL (block lists) but I
was intrigued by the idea of having Sendmail process it, rather than have
a procmail process generate overhead to reference yet another block list.
Sendmail supports DNSBL's using the dnsbl FEATURE. In your mc file (all
one line, wrapped by my MUA):
FEATURE(`dnsbl',`blacklist.zone.tld',`" Mail from "$&{client_addr}"
rejected; see
<http://www.your-website.tld/policy/abuse.html?IP="$&{client_addr}"\#DNSBLNAME>
for an explanation."')dnl
That error text is a genericised version of the one I use - I have an abuse
page which has dynamic links to the lookup engines for each DNSBL I employ,
and by merit of people hitting the site using the link, I have a weblog
entry showing who is checking on bounces. This beats just telling them
they got rejected because of some particular DNSBL and havintg them sort
out what IP, whatever - when a live human actually gets blocked, it's nice
to not complicate matters for them - they no doubt already feel put out enough.
I find however that not too many live humans get blocked by the small list
of DNSBLs I use...
Before using a DNSBL at the SMTP level, you might consider using it at the
procmail level to see which DNSBL lists flag your junkmail but not your
legitimate mail, THEN choose which one(s) you want to employ at the STMP
level (and of course, remove the testing stuff from your procmail setup).
Before you think "gosh, I can just write a testing procmailrc and pump a
bunch of saved mail at it", think again: DNSBLs are dynamic things, and
hosts responsible for sending spam you recieved some time ago may not be
listed anymore, just as hosts you've received legitimate mail from in the
past may not be categorized as spammers. Country lists (nerd.dk), and
dialup user lists though should be constant enough that you won't have a
lot of mis-files based on older messages, though these DNSBLs aren't for
identifying spam per-se.
I run with the delay_checks FEATURE in Sendmail, which delays RBL checks
until after AUTH (and after checking the access db). This also has the
benefit of obtaining the intended recipient list before rejecting the message.
---
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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