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********************************
* SHOULD YOU USE THIS PACKAGE? *
********************************

Since version 4.50, Exim has the content-scanning extension formerly
known as "exiscan" built-in. It has a number of advantages and
disadvantages compared to SA-Exim.

Advantages of built-in content-scanning interface:

 * One less configuration file to edit.
 * Spam control policy integrates better with Exim's ACL system.
 * It's possible to tell SA which user to scan for (the -u parameter of
   spamc). SA-Exim can't do that (yet).
 * Finer control over the mail header is possible, but not in a clean
   way (it involves putting all header fields you might possibly want
   to add in the report template, and using rather complicated
   expansion expressions to extract the wanted ones from
   $spam_report). At any rate, you can choose a prefix different from
   "X-Spam-".

Advantages of SA-Exim:

 * It is possible to use the report_safe feature, which turns mail
   deemed to be spam into a message/rfc822 attachment of a report
   message. (Note however that if you do, then any X-SA-* fields added
   to help the greylisting module can't be removed.)
 * All the add_header and rewrite_header options in 
   /etc/spamassassin/local.cf will be obeyed. In other words,
   everything will be *almost* as if you filtered the mail through 
   spamassassin on the command line.
 * So-called teergrubing ("tarpitting") is possible in a way that
   isn't possible with exiscan (I'm not in any way saying that it
   works as a counterattack against spammers).
 * You can simply add the sa-exim package to a standard exim4
   installation and it should, in principle, instantly work (except
   you have to uncomment one line in sa-exim.conf).

Both alternatives enable you to defer, greylist, reject, and blackhole
mail, optionally saving copies, at configurable score levels.

*****************
* CONFIGURATION *
*****************

This version of the sa-exim package defaults to placing a configuration
sniplet in /etc/exim4/conf.d/. Depending on what you have answered to the
DebConf questions while configuring Exim4, the module will be loaded
automatically, or human intervention is required.

To find out what configuration file Exim4 is using, issue:

  $ exim4 -bV | tail -1
  Configuration file is /path/to/configfile

If /path/to/configfile shows:

  - /etc/exim4/exim4.conf
    You are using the hand-crafted configuration file.
        See the 'HAND-CRAFTED' section below.
        
  - /var/lib/exim4/config.autogenerated 
    You are using the debianized configuration scheme - with either
    'split' or 'unsplit' configuration file.
        See the 'DEBIANIZED' section below.


HAND-CRAFTED
------------

Use 'grep "local_scan_path" /etc/exim4/exim4.conf" to see if the sa-exim
line is included in the configuration. If grep returns something, check
if it matches the following line. If grep returns nothing, you have to
manually add the following line to the exim4.conf file and restart exim4.

    local_scan_path = /usr/lib/exim4/local_scan/sa-exim.so

Change or add the line above and manually restart exim4 by issuing
'invoke-rc.d exim4 reload' or '/etc/init.d/exim4 reload' as root.


DEBIANIZED
----------

Use 'grep "local_scan_path" /var/lib/exim4/config.autogenerated' to
see if the sa-exim line is included in the configuration. If grep
returns something, you're set and already using the sa-exim module. If
grep returns nothing, we need to figure out a few things:

Issue:
        $ grep "use_split_config" /etc/exim4/update-exim4.conf.conf 
      dc_use_split_config='true'

If your result shows 'false' where mine shows 'true', then you're
using the unsplit configuration, generated from
/etc/exim4/exim4.conf.template.  If you haven't customized that file
you could edit /etc/exim4/update-exim4.conf.conf by hand, change the
'false' to 'true' and issue 'update-exim4.conf' as root. Then, check
again if the sa-exim module line is included. It should. If it still
isn't: mail me. If it is, restart exim4 by issuing 'invoke-rc.d exim4
restart' or '/etc/init.d/exim4 restart' as root. If you *have*
customized /etc/exim4/exim4.conf.template, then you'd better stick
with the unsplit configuration scheme and add the local_scan_path
setting by hand, like with the hand-crafted configuration file.

Next, read all about greylisting and sa-exim:

***************
* GREYLISTING *
***************
Notes on greylisting with sa-exim.

If you use SpamAssassin 3.0 or better, you do not need to patch it, you
can just use the Greylisting module shipped with sa-exim. 
The only thing you need to do to enable it, is to copy the 4 lines below
loadplugin in the greylisting README, and adjust the score if you wish (see
README.Greylisting for details).

***********************************
* PROBLEMS WITH BAYES AUTO-EXPIRY *
***********************************

When scanning mail during the SMTP dialogue there is somewhat limited
time before the remote host gives up, even if they should wait for at
least ten minutes. To avoid Exim returning a temporary error status,
or the remote host giving up prematurely and in some cases for good,
SA-Exim overrides Exim's timeout handler and accepts the message if
SpamAssassin takes too long, by default 240 seconds.

Using SpamAssassin's Bayesian learning module means that it will
automatically expire old tokens when its database has grown too large.
That can take several minutes. If it takes too long, SA-Exim will
abort it, meaning that SpamAssassin will run auto-expiry again next
time, and be aborted, and so on...

If this happens, you have a few remedies:

1) Set SAtimeout to a higher value in /etc/exim4/sa-exim.conf.

2) Run sa-learn --force-expire periodically. How you run it depends on
   how you've configured SpamAssassin. Running it as Debian-exim may
   be sufficient.

2 a) In addition, you can add

   bayes_auto_expire 0

   to /etc/spamassassin/local.cf. This may not be a good idea if
   SpamAssassin, for whatever reason, is also used as a more
   traditional filter from e.g. .procmailrc, as all users will need to
   run sa-learn --force-expire then.

2 b) If you get a lot of mail, consider adding

   bayes_learn_to_journal 1

   to local.cf. See the Mail::SpamAssassin::Conf(3) manual page for
   more information.

**********************************
* NOTICE ABOUT SPAMC CONFIG FILE *
**********************************

Recent versions of spamc can read command-line parameters and switches
from a configuration file called /etc/spamassassin/spamc.conf. If that
file specifies conflicting options, it will prevent SA-Exim from 
working. For now, you'll have to make sure that it doesn't.

 -- Magnus Holmgren <holmgren@debian.org>, Tue, 24 Jun 2008 14:27:59 +0200