Bug#290464: SPF setup

[Robert Millan]

FWIW, here's a short recipe to setup SPF on debian exim packages (much
easier than setting up spfd imho):

  apt-get install libmail-spf-query-perl

Reconfigure exim4-config with "split small files" option.

Add this blurb to 30_exim4-config_check_rcpt, right after "acl_check_rcpt:"

  # Use "spfquery" to obtain SPF status for this particular sender/host.
  # If the return code of that command is 1, this is an unauthorized sender.
  #
  deny
    message     = [SPF] $sender_host_address is not allowed to send mail from $sender_address_domain.  \
                  Please see http://www.openspf.org/why.html?sender=$sender_address&ip=$sender_host_address
    log_message = SPF check failed.
    set acl_m9  = -ip=$sender_host_address \
                  -sender=$sender_address \
                  -helo=\"$sender_helo_name\"
    set acl_m9  = ${run{/usr/bin/spfquery $acl_m9}}
    condition   = ${if eq {$runrc}{1}{true}{false}}

NOTE: If you use sarge, you might need to move the relay/auth "accept" ACLs
  up from the bottom of this file, to avoid performing SPF checks on your own
  mail agents.

-- 
Robert Millan