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Subject: Fighting email spam and anti-UBE pointers
This article was archived around: 23 May 2006 04:24:40 GMT
Posting-Frequency: 2 times a month
Maintainer: Jari Aalto A T cante net
Announcement: "Bounces, Challenge-response systems, MTA, Bayesian tools (article pointer)"
FAQ archive is at http://www.faqs.org/faqs/
This message is an excerpt from bigger from Procmail Module
Library project's README.html document titled "Procmail
strategies against spam." available at
The key points discussed in the document:
- Auto-replying or bouncing is considered a bad tactic
- MTA rejects can be abused and system administrators should
check their setup at least in regard to viruses.
- Challenge-Response system is based on false assumption that sender's
address can be used for authentication. It cannot and thus any C-R
system will contribute nothing else by amplifying the spam problem.
See picture http://pm-lib.sourceforge.net/pic/cr-system-joe-job.png
What should be done then?
- Bayesian tools are non-intrusive, harm no third parties
(in contrast to C-R), are easy to use and provide a good shelter.
- Battery of bayesian tools give even better shield due to
each program using a slightly different algorithm.
Many clarifying pictures are included:
- How address harvesting works
- How viruses should not be treated (at MTA level)
- Challenge-Response based authentication (overview)
- Challenge-Response system causing "Joe-Job"
- How MTA level UBE prevention works
- Procmail with battery of statistical tools
Table of contents:
1.0 Thoughts about increasing spam annoyance
1.1 Bouncing messages do no good
1.2 Rule based systems are not the solution
1.3 Challenge-Response systems make matters worse
1.3.1 Challenge-Response is not a doorbell but a
gun shooting decoys
1.3.2 Questioning Challenge-Response systems implementations
1.3.3 Summary - What are the effects of Challenge-Response
1.4 Spam appearing in your yard - a story
2.0 A lightweight UBE block system with pure procmail
2.1 Suitable for accounts which ...
2.2 Where to put "pure procmail" UBE checks?
2.3 Using Procmail Module Library to fight spam
3.0 A heavyweight UBE blocking system
3.1 Advice for Debian Exim 4 mail system administrator
3.2 Advice for the normal account
3.3 Configuring Bayesian programs
3.4 A heavyweight spam catch setup using procmail
._UBE_ = Unsolicited Bulk Email
._UCE_ = (subset of UBE) Unsolicited Commercial Email
_Spam_ = Spam describes a particular kind of Usenet posting (and
canned spiced ham), but is now often used to describe many kinds of
inappropriate activities, including some email-related events. It
is technically incorrect to use "spam" to describe email abuse,
although attempting to correct the practice would amount to tilting
_Spam_ = definition by Erik Beckjord. "Some people decide that Spam
is anything you decide you want to ban if you can't handle the
intellectual load on a list." Remember, not to be confused with
real spam, which is unwanted bulk mail.
People are nowadays seeking a cure which will stop
or handle UBE. That can be easily done with procmail (under your
control) and with sendmail (by your sysadm). In order to select the
right strategy against UBE messages, you should read this section
and then decide how you will be using your procmail to deal with it.