<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML ><HEAD ><TITLE >Spam Filtering for Mail Exchangers</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="NEXT" TITLE="Introduction" HREF="introduction.html"><META NAME="KEYWORD" CONTENT="anti-spam"><META NAME="KEYWORD" CONTENT="anti-virus"><META NAME="KEYWORD" CONTENT="bogus virus warnings"><META NAME="KEYWORD" CONTENT="collateral spam"><META NAME="KEYWORD" CONTENT="delivery status notification"><META NAME="KEYWORD" CONTENT="dsn"><META NAME="KEYWORD" CONTENT="exim"><META NAME="KEYWORD" CONTENT="exim4"><META NAME="KEYWORD" CONTENT="exiscan"><META NAME="KEYWORD" CONTENT="exiscan-acl"><META NAME="KEYWORD" CONTENT="greylisting"><META NAME="KEYWORD" CONTENT="junk mail"><META NAME="KEYWORD" CONTENT="sa-exim"><META NAME="KEYWORD" CONTENT="smtp"><META NAME="KEYWORD" CONTENT="spam"><META NAME="KEYWORD" CONTENT="spamassassin"><META NAME="KEYWORD" CONTENT="teergrubing"><META NAME="KEYWORD" CONTENT="transaction delay"></HEAD ><BODY CLASS="book" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="BOOK" ><A NAME="AEN1" ></A ><DIV CLASS="TITLEPAGE" ><H1 CLASS="title" ><A NAME="AEN2" ></A >Spam Filtering for Mail Exchangers</H1 ><H2 CLASS="subtitle" >How to reject junk mail in incoming SMTP transactions.</H2 ><H3 CLASS="author" ><A NAME="AEN6" ></A >Tor Slettnes</H3 ><DIV CLASS="affiliation" ><DIV CLASS="address" ><P CLASS="address" ><TT CLASS="email" ><<A HREF="mailto:tor@slett.net" >tor@slett.net</A >></TT ></P ></DIV ></DIV ><H4 CLASS="EDITEDBY" >Edited by</H4 ><H3 CLASS="editor" >Joost De Cock</H3 ><H3 CLASS="editor" >Devdas Bhagat</H3 ><H3 CLASS="editor" >Tom Wright</H3 ><P CLASS="edition" >Version 1.0 -- Release Edition </P ><HR></DIV ><DIV CLASS="TOC" ><DL ><DT ><B >Table of Contents</B ></DT ><DT ><A HREF="introduction.html" >Introduction</A ></DT ><DD ><DL ><DT >1. <A HREF="intro-purpose.html" >Purpose of this Document</A ></DT ><DT >2. <A HREF="intro-audience.html" >Audience</A ></DT ><DT >3. <A HREF="intro-updates.html" >New versions of this document</A ></DT ><DT >4. <A HREF="intro-history.html" >Revision History</A ></DT ><DT >5. <A HREF="intro-credits.html" >Credits</A ></DT ><DT >6. <A HREF="intro-feedback.html" >Feedback</A ></DT ><DT >7. <A HREF="intro-translations.html" >Translations</A ></DT ><DT >8. <A HREF="intro-copyright.html" >Copyright information</A ></DT ><DT >9. <A HREF="intro-prerequisites.html" >What do you need?</A ></DT ><DT >10. <A HREF="intro-conventions.html" >Conventions used in this document</A ></DT ><DT >11. <A HREF="intro-organization.html" >Organization of this document</A ></DT ></DL ></DD ><DT >1. <A HREF="background.html" >Background</A ></DT ><DD ><DL ><DT >1.1. <A HREF="whysmtptime.html" >Why Filter Mail During the SMTP Transaction?</A ></DT ><DT >1.2. <A HREF="goodbadugly.html" >The Good, The Bad, The Ugly</A ></DT ><DT >1.3. <A HREF="smtpintro.html" >The SMTP Transaction</A ></DT ></DL ></DD ><DT >2. <A HREF="techniques.html" >Techniques</A ></DT ><DD ><DL ><DT >2.1. <A HREF="smtpdelays.html" >SMTP Transaction Delays</A ></DT ><DT >2.2. <A HREF="dnschecks.html" >DNS Checks</A ></DT ><DT >2.3. <A HREF="smtpchecks.html" >SMTP checks</A ></DT ><DT >2.4. <A HREF="greylisting.html" >Greylisting</A ></DT ><DT >2.5. <A HREF="senderauth.html" >Sender Authorization Schemes</A ></DT ><DT >2.6. <A HREF="datachecks.html" >Message data checks</A ></DT ><DT >2.7. <A HREF="collateral.html" >Blocking Collateral Spam</A ></DT ></DL ></DD ><DT >3. <A HREF="considerations.html" >Considerations</A ></DT ><DD ><DL ><DT >3.1. <A HREF="multimx.html" >Multiple Incoming Mail Exchangers</A ></DT ><DT >3.2. <A HREF="otherservers.html" >Blocking Access to Other SMTP Servers</A ></DT ><DT >3.3. <A HREF="forwardedmail.html" >Forwarded Mail</A ></DT ><DT >3.4. <A HREF="usersettings.html" >User Settings and Data</A ></DT ></DL ></DD ><DT >4. <A HREF="qanda.html" >Questions & Answers</A ></DT ><DT >A. <A HREF="exim.html" >Exim Implementation</A ></DT ><DD ><DL ><DT >A.1. <A HREF="exim-prereq.html" >Prerequisites</A ></DT ><DT >A.2. <A HREF="exim-configfile.html" >The Exim Configuration File</A ></DT ><DT >A.3. <A HREF="exim-options.html" >Options and Settings</A ></DT ><DT >A.4. <A HREF="exim-firstpass.html" >Building the ACLs - First Pass</A ></DT ><DT >A.5. <A HREF="exim-smtpdelays.html" >Adding SMTP transaction delays</A ></DT ><DT >A.6. <A HREF="exim-greylisting.html" >Adding Greylisting Support</A ></DT ><DT >A.7. <A HREF="exim-spf.html" >Adding SPF Checks</A ></DT ><DT >A.8. <A HREF="exim-mime.html" >Adding MIME and Filetype Checks</A ></DT ><DT >A.9. <A HREF="exim-av.html" >Adding Anti-Virus Software</A ></DT ><DT >A.10. <A HREF="exim-sa.html" >Adding SpamAssassin</A ></DT ><DT >A.11. <A HREF="exim-sign.html" >Adding Envelope Sender Signatures</A ></DT ><DT >A.12. <A HREF="exim-bounces.html" >Accept Bounces Only for Real Users</A ></DT ><DT >A.13. <A HREF="exim-forward.html" >Exempting Forwarded Mail</A ></DT ><DT >A.14. <A HREF="exim-final.html" >Final ACLs</A ></DT ></DL ></DD ><DT ><A HREF="gloss.html" >Glossary</A ></DT ><DT >B. <A HREF="gpl.html" >GNU General Public License</A ></DT ><DD ><DL ><DT >B.1. <A HREF="gpl-1.html" >Preamble</A ></DT ><DT >B.2. <A HREF="gpl-2.html" >TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION</A ></DT ><DT >B.3. <A HREF="gpl-3.html" >How to Apply These Terms to Your New Programs</A ></DT ></DL ></DD ></DL ></DIV ><DIV CLASS="LOT" ><DL CLASS="LOT" ><DT ><B >List of Tables</B ></DT ><DT >1. <A HREF="intro-conventions.html#conventiontable" >Typographic and usage conventions</A ></DT ><DT >1-1. <A HREF="smtpintro.html#smtpdialogue" >Simple SMTP dialogue</A ></DT ><DT >A-1. <A HREF="exim-smtpdelays.html#aclvarusage" >Use of ACL connection/message variables</A ></DT ></DL ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" > </TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="introduction.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" > </TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Introduction</TD ></TR ></TABLE ></DIV ></BODY ></HTML >