This file contains suggestions on how to get SpamAssassin working
sitewide with Exim 3, submitted by John Girash
<girash@skyron.harvard.edu>. Please note that this is not the easiest
way to integrate spamassassin into your mail stream (simple procmail
is; see procmailrc.example).

Here's my writeup of how I got SpamAssassin working under exim3, including
user-level mail filtering via an exim filter file.  Most credit goes to "dman"
(formerly at <dman@dman.ddts.net>) for providing an earlier version of this
document; I merely updated it for the more-current versions (exim 3.35-1 and
spamassassin 2.53-1; I use Debian).

Step 1 :
Edit /etc/exim/exim.conf to include scanning (filtering) by spamassassin
in the delivery of a message.  In the Transports section add the following
(order is irrelevant, and you can omit the leading 2 spaces of each line):

  # Spam Assassin 2.53 for exim3
  #   Notes :
  #   This pipes the message to exim using the BSMTP (batched SMTP)
  #   protocol. This avoids any nasties with shell metacharacters in
  #   addresses. Prior to giving the message back to itself, exim will
  #   filter it through the 'spamc' command. As the message returns to exim,
  #   the "received_protocol" set to "spam-scanned".

  spamcheck:
    driver = pipe

    command = /usr/sbin/exim -oMr spam-scanned -bS
    transport_filter = /usr/bin/spamc -u ${local_part}

    bsmtp = all

    home_directory = "/tmp"
    current_directory = "/tmp"

    # must use a privileged user to set $received_protocol on the way back in!
    user = mail
    group = mail

    return_path_add = false

    log_output = true
    return_fail_output = true

    prefix =
    suffix =

Insert the following at the top of the Directors section :

  # Spam Assassin 2.53 for exim3
  #   This director is used for any message that
  #   * wasn't received from spamassassin (determined by $received_protocol)
  #   * wasn't received via a pipe from a local user
  #   * isn't already flagged (this is safe because the only flag that is
  #      skipped is a positive flag; spammers can tag their spam for you,
  #      but they can't tag it as being clean).#

  spamcheck_director:

    # do not use this director when verifying a local-part at SMTP-time
    no_verify

    condition = "${if and { {!def:h_X-Spam-Flag:} {!eq {$received_protocol}{spam-scanned}} {!eq {$received_protocol}{local}} } {1}{0}}"
    driver = smartuser
    transport = spamcheck

Step 2:

Edit /etc/default/spamassassin to start 'spamd' at boot time. I just
left the "-m 10" in as Debian's defaults had, but removed the "-c"
that would otherwise create user preferences files, as that's how dman
had his set up.

  # Change to one to enable spamd
  ENABLED=1
  OPTIONS="-m 10"

Step 3:

Start spamd as root :
# /etc/init.d/spamassassin start

That's it! Now SpamAssassin will check all your mail & put in header
info stating whether or not SpamAssassin thinks any given message is
spam or not. To achieve actual filtering, I do as dman says & use an
exim filter file in my user account, i.e. a file named "~/.forward"
that has as its first line "# Exim filter". The following is my full
.forward file:

  #   Exim filter   <<== do not edit or remove this line!
  if
    $h_X-Spam-Status: contains "Yes, hit"
        or
    "${if def:h_X-Spam-Flag {def}{undef}}" is "def"
  then
    save $home/Mail/junk/autospam.mai
    finish
  endif

This dumps all messages tagged as spam into file
~/Mail/junk/autospam.mai . You want to keep this around (as opposed to
sending to /dev/null) because while SpamAssassin produces almost no
false positives, it does produce some. I search on "Yes, hit" instead
of just "Yes" because once SpamAssassin has read enough mail to start
doing "Bayesian" filtering, it inserts the test name "BAYES" into the
headers of most messages, whether spam or not.

If you want your .forward file to also act like a traditional one and
forward your mail to a different address, simply append the line
"deliver address@machine.dom" to the end of the above, replacing
address@machine.dom with the address of the new destination you want.

dman says: "Note that because I skip scanning on messages with an
X-Spam-Flag: header I must check for that in my filter. Otherwise a
spammer could put the X-Spam-Flag: header in but omit the
X-Spam-Status: header and slip past my filter. For details on what a
filter file is and where it goes see sections 24.7 (specifically the
'filter' option) and 50.3 of spect.txt and section 5 of filter.txt."
(...I usually just do a google search myself.)

Much thanks to dman <dman@dman.ddts.net>, whose similar document
(http://dman.ddts.net/~dman/config_docs/exim3_spamassassin.html)
regarding using exim3 with earlier versions of SpamAssassin (<=2.11)
helped me to no end (and from which I borrow liberally here). He also
thanks the following folks for helping him, so it seems proper to
mention them here: * Nigel Metheringham, * Kevin Fleming and * Renee
Brown.