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######################################################################
# ACL CONFIGURATION #
# Specifies access control lists for incoming SMTP mail #
######################################################################
begin acl
# This access control list is used for every RCPT command in an incoming
# SMTP message. The tests are run in order until the address is either
# accepted or denied.
acl_check_rcpt:
# Accept if the source is local SMTP (i.e. not over TCP/IP). We do this by
# testing for an empty sending host field.
accept hosts = :
control = dkim_disable_verify
#############################################################################
# The following section of the ACL is concerned with local parts that contain
# @ or % or ! or / or | or dots in unusual places.
#
# The characters other than dots are rarely found in genuine local parts, but
# are often tried by people looking to circumvent relaying restrictions.
# Therefore, although they are valid in local parts, these rules lock them
# out, as a precaution.
#
# Empty components (two dots in a row) are not valid in RFC 2822, but Exim
# allows them because they have been encountered. (Consider local parts
# constructed as "firstinitial.secondinitial.familyname" when applied to
# someone like me, who has no second initial.) However, a local part starting
# with a dot or containing /../ can cause trouble if it is used as part of a
# file name (e.g. for a mailing list). This is also true for local parts that
# contain slashes. A pipe symbol can also be troublesome if the local part is
# incorporated unthinkingly into a shell command line.
#
# Two different rules are used. The first one is stricter, and is applied to
# messages that are addressed to one of the local domains handled by this
# host. The line "domains = +local_domains" restricts it to domains that are
# defined by the "domainlist local_domains" setting above. The rule blocks
# local parts that begin with a dot or contain @ % ! / or |. If you have
# local accounts that include these characters, you will have to modify this
# rule.
deny message = Restricted characters in address
domains = +local_domains
local_parts = ^[.] : ^.*[@%!/|]
# The second rule applies to all other domains, and is less strict. The line
# "domains = !+local_domains" restricts it to domains that are NOT defined by
# the "domainlist local_domains" setting above. The exclamation mark is a
# negating operator. This rule allows your own users to send outgoing
# messages to sites that use slashes and vertical bars in their local parts.
# It blocks local parts that begin with a dot, slash, or vertical bar, but
# allows these characters within the local part. However, the sequence /../
# is barred. The use of @ % and ! is blocked, as before. The motivation here
# is to prevent your users (or your users' viruses) from mounting certain
# kinds of attack on remote sites.
deny message = Restricted characters in address
domains = !+local_domains
local_parts = ^[./|] : ^.*[@%!] : ^.*/\\.\\./
#############################################################################
# Accept mail to postmaster in any local domain, regardless of the source,
# and without verifying the sender.
accept local_parts = postmaster
domains = +local_domains
# Deny unless the sender address can be verified.
require verify = sender
# Accept if the message comes from one of the hosts for which we are an
# outgoing relay. It is assumed that such hosts are most likely to be MUAs,
# so we set control=submission to make Exim treat the message as a
# submission. It will fix up various errors in the message, for example, the
# lack of a Date: header line. If you are actually relaying out out from
# MTAs, you may want to disable this. If you are handling both relaying from
# MTAs and submissions from MUAs you should probably split them into two
# lists, and handle them differently.
# Recipient verification is omitted here, because in many cases the clients
# are dumb MUAs that don't cope well with SMTP error responses. If you are
# actually relaying out from MTAs, you should probably add recipient
# verification here.
# Note that, by putting this test before any DNS black list checks, you will
# always accept from these hosts, even if they end up on a black list. The
# assumption is that they are your friends, and if they get onto a black
# list, it is a mistake.
accept hosts = +relay_from_hosts
control = submission
control = dkim_disable_verify
# Accept if the message arrived over an authenticated connection, from
# any host. Again, these messages are usually from MUAs, so recipient
# verification is omitted, and submission mode is set. And again, we do this
# check before any black list tests.
accept authenticated = *
control = submission
control = dkim_disable_verify
# Insist that a HELO/EHLO was accepted.
require message = nice hosts say HELO first
condition = ${if def:sender_helo_name}
# Insist that any other recipient address that we accept is either in one of
# our local domains, or is in a domain for which we explicitly allow
# relaying. Any other domain is rejected as being unacceptable for relaying.
require message = relay not permitted
domains = +local_domains : +relay_to_domains
# We also require all accepted addresses to be verifiable. This check will
# do local part verification for local domains, but only check the domain
# for remote domains. The only way to check local parts for the remote
# relay domains is to use a callout (add /callout), but please read the
# documentation about callouts before doing this.
require verify = recipient
#############################################################################
# There are no default checks on DNS black lists because the domains that
# contain these lists are changing all the time. However, here are two
# examples of how you can get Exim to perform a DNS black list lookup at this
# point. The first one denies, whereas the second just warns.
#
# deny message = rejected because $sender_host_address is in a black list at $dnslist_domain\n$dnslist_text
# dnslists = black.list.example
#
# warn dnslists = black.list.example
# add_header = X-Warning: $sender_host_address is in a black list at $dnslist_domain
# log_message = found in $dnslist_domain
#############################################################################
#############################################################################
# This check is commented out because it is recognized that not every
# sysadmin will want to do it. If you enable it, the check performs
# Client SMTP Authorization (csa) checks on the sending host. These checks
# do DNS lookups for SRV records. The CSA proposal is currently (May 2005)
# an Internet draft. You can, of course, add additional conditions to this
# ACL statement to restrict the CSA checks to certain hosts only.
#
# require verify = csa
#############################################################################
# At this point, the address has passed all the checks that have been
# configured, so we accept it unconditionally.
accept
# This ACL is used after the contents of a message have been received. This
# is the ACL in which you can test a message's headers or body, and in
# particular, this is where you can invoke external virus or spam scanners.
# Some suggested ways of configuring these tests are shown below, commented
# out. Without any tests, this ACL accepts all messages. If you want to use
# such tests, you must ensure that Exim is compiled with the content-scanning
# extension (WITH_CONTENT_SCAN=yes in Local/Makefile).
acl_check_data:
# Deny if the message contains an overlong line. Per the standards
# we should never receive one such via SMTP.
#
deny message = maximum allowed line length is 998 octets, \
got $max_received_linelength
condition = ${if > {$max_received_linelength}{998}}
# Deny if the message contains a virus. Before enabling this check, you
# must install a virus scanner and set the av_scanner option above.
#
# deny malware = *
# message = This message contains a virus ($malware_name).
# Add headers to a message if it is judged to be spam. Before enabling this,
# you must install SpamAssassin. You may also need to set the spamd_address
# option above.
#
# warn spam = nobody
# add_header = X-Spam_score: $spam_score\n\
# X-Spam_score_int: $spam_score_int\n\
# X-Spam_bar: $spam_bar\n\
# X-Spam_report: $spam_report
# Accept the message.
accept
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