On Thu, Feb 20, 2003 at 11:07:25PM -0600, Dan Nelson wrote:
> In the last episode (Feb 20), Dragoncrest said:
> > Hmm.  I'm trying to avoid using Procmail at all costs since we're
> > currently on a Sendmail/Qpopper configuration that I can work with. 
> > But it may turn out that the only way around this IS to go with that. 
> > Thing is, I'd like to stick with what we have and make it work with
> > that rather than totally ripping our our MTA and throwing in a whole
> > brand new one we know nothing about.
> Procmail is not an mta; it's an email filter.  It's usually launched
> from the .forward file, but you can configure sendmail to use procmail
> as the default local mail delivery agent, or you can run it standalone
> (procmail < message.txt) if you don't want it to be part of the mail
> delivery process at all.
Mmm. Two things here, one is no you should definitely not go around
messing inside mailboxes with hand-written scripts; it is not just a
simple case of getting at the message, removing it and all will be well.
You have to take on board all sorts of probems like file-locking, like
the testing of pathological cases, and the fact you are possibly going
to be content inspecting mail concerning other people.

I presume you are trying to de-spam the incoming mail. This cannot be
done without some not inconsiderable effort.

Some of it you can do with your MTA (yours is sendmail I take it), by
the use of RBL (blacklist lookups for known spammers). Some of it can be
done by an MDA (such as procmail), and some of it can be better served
by the use of a spam-marking program such as spamassassin. You may also
want virus checking in it by the use of Amavis or some-such. In fact you
may end up doing checks at all sorts of levels during the delivery

And then you have to decide what to do with the "spam", since
false-positives are possible. Your MUA (whatever you use to read the
mail may also have to have filter rules).

All in all this is not a 5 minute job. The majority of spam in the world
comes mainly from an estimated number of sources to be less than 200,
the number of people trying to give solutions to this must be quadruple
that number at least !

As pointed out above, procmail is not an MTA , techinically it is an
MDA, a delivery agent. It can be set up on a per-user basis or
system-wide. It can itself filter the mail into another program like
spamassassin and so on.

There is a lot of work involved in this, I know I have been busy for
a long time on it...and I am not running a corporate server !

You will need to do some investigations..asking here, looking at
solutions people have implemented. But no solutions are going to 100%
solve the problem, you can reduce it greatly by using the methods I
mention above.

I know zilch about sendmail, but I know that the new version of Postfix,
which I have yet to try, does allow for tight integration of these
various things..maybe also with sendmail...I don't know.

For reference: I use Postfix as MTA, Amavis/Antivir as virus checker,
and procmail recipes to use spamassassin to do spam checks. Even with an
artificially low threshold for spam marking I am getting maybe 1 false
positive spam a day, when I bump the threshold up to something more
realistic I would expect that to further drop.

   Cliff Sarginson 
   The Netherlands

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