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Re: [K12OSN] OT: just reduced spam by 95% with Free Software



There are no false positives; that's the beauty of it. 

OpenBSD spamd doesn't analyze the email content in the way that, say, SpamAssassin would do, so it doesn't care what kind of content is in an email.  Rather, it judges whether *the sender itself* is a spammer.  Legitimate email from a sender whose IP address isn't blocked by your blacklist will *always* make it through.  That's because legitimate email servers always follow RFC 821 and try again after getting initially greylisted.  Only mailers that "pump and dump", i. e. send once and don't bother trying again (a quite blatant violation of RFC 821) will not get past a greylist.  Who practices this silliness?  You guessed it, spammers.

There's an important note here.  As some people have correctly pointed out, greylisting definitely helps, but it is not *by itself* a complete solution, nor was it meant to be.  This is why OpenBSD spamd also includes something called "greytrapping", as well as tarpitting.  I make very effective use of greytrapping, and it has cut down my spam so much, it's incredible.  The tarpitting also makes quite a few "pump and dump" spammers disconnect the SMTP session and go away.  Legitimate mailers will not have a problem, only spammers.

The "Part I" link goes into some detail about this.

--TP
_______________________________
Do you GNU!?
Microsoft Free since 2003--the ultimate antivirus protection!


Peter Hartmann wrote:
Wait....so how does it deal with false positives?  is it that non-spam
gets resent and then that makes it through?

Thanks,
Peter

On 4/12/07, "Terrell Prudé Jr." <microman cmosnetworks com> wrote:

 Here you go.  Hope it helps someone.  It's been two and a half months now,
and it sure helped me.

 PART I:
http://applications.linux.com/article.pl?sid=07/03/28/1522252&tid=115

 PART II:
 http://www.linux.com/article.pl?sid=07/03/28/1631206

 --TP


_______________________________
 Do you GNU!?
 Microsoft Free since 2003--the ultimate antivirus protection!


 Terrell Prudé Jr. wrote:
 I will write up a document on this and email it to the list, then.

 --TP

_______________________________
 Do you GNU!?
 Microsoft Free since 2003--the ultimate antivirus protection!


 Huck wrote:
Terrell...more info please? ;)

 --Huck

 Terrell Prudé Jr. wrote:

Folks,

 I will first admit that this is somewhat off-topic from K12LTSP.  That
said, schools could benefit from this.  This is definitely applicable for
those of you who asked about using K12LTSP as an email server for your
students.

 We all know about the spam problem.  Well, over this last week, I have been
playing with OpenBSD's spamd as a possible solution.  Basically, I put the
spamd box in front of my (yes, GNU/Linux) email server.  I have now reduced
the spam count in my inbox from close to 200 a day down to...five.  FIVE.
This is without false positives.  I have verified that by studying my spamd
logs all week and comparing them to my real email server's logs.

 For those of you with small pipes to the Internet, this is *definitely*
something you might want to consider.  It saves you some bandwidth.

 If anyone's interested, let me know.

 --TP
 _______________________________
 Do you GNU!?
 Microsoft Free since 2003 <http://www.gnu.org/>--the ultimate antivirus
protection!


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