好了，打起精神来！ 这篇文章很长 - 但恭喜你读到这里！
以下 ACL 包含了我们在这个实现中描述的所有检查。 但是，有些已被注释掉，原因如下：
灰名单。 这要么需要安装额外的软件，要么通过 Exim 配置文件中的额外 ACL 和定义进行相当复杂的内联配置。 不过，我强烈推荐它。
病毒扫描。 没有像 SpamAssassin 那样几乎每个人都使用的普遍扫描器来进行垃圾邮件识别。 另一方面，随附的文档Exiscan-ACL应该很容易理解。
SpamAssassin 的用户设置。 这对许多人来说是不可接受的权衡，因为它涉及到将邮件延迟到除邮件的第一个收件人之外的所有人。
信封发件人签名。 这会产生一些后果，例如对于漫游用户。 此外，它还涉及到配置路由器和传输以及 ACL。 有关详细信息，请参阅该部分。
仅接受真实用户的退回邮件。 有几种方法可以做到这一点，并且确定哪些用户是真实的，这取决于邮件的传递方式。
废话不多说，这是我们一直等待的最终结果。
# This access control list is used at the start of an incoming
# connection. The tests are run in order until the connection is
# either accepted or denied.
acl_connect:
# Record the current timestamp, in order to calculate elapsed time
# for subsequent delays
warn
set acl_m2 = $tod_epoch
# Accept mail received over local SMTP (i.e. not over TCP/IP). We do
# this by testing for an empty sending host field.
# Also accept mails received over a local interface, and from hosts
# for which we relay mail.
accept
hosts = : +relay_from_hosts
# If the connecting host is in one of several DNSbl's, then prepare
# a warning message in $acl_c1. We will later add this message to
# the mail header. In the mean time, its presence indicates that
# we should keep stalling the sender.
#
warn
!hosts = ${if exists {/etc/mail/whitelist-hosts} \
{/etc/mail/whitelist-hosts}}
dnslists = list.dsbl.org : \
dnsbl.sorbs.net : \
dnsbl.njabl.org : \
bl.spamcop.net : \
dsn.rfc-ignorant.org : \
sbl-xbl.spamhaus.org : \
l1.spews.dnsbl.sorbs.net
set acl_c1 = X-DNSbl-Warning: \
$sender_host_address is listed in $dnslist_domain\
${if def:dnslist_text { ($dnslist_text)}}
# Likewise, if reverse DNS lookup of the sender's host fails (i.e.
# there is no rDNS entry, or a forward lookup of the resulting name
# does not match the original IP address), then generate a warning
# message in $acl_c1. We will later add this message to the mail
# header.
warn
condition = ${if !def:acl_c1 {true}{false}}
!verify = reverse_host_lookup
set acl_m9 = Reverse DNS lookup failed for host $sender_host_address
set acl_c1 = X-DNS-Warning: $acl_m9
# Accept the connection, but if we previously generated a message in
# $acl_c1, stall the sender until 20 seconds has elapsed.
accept
set acl_m2 = ${if def:acl_c1 {${eval:20 + $acl_m2 - $tod_epoch}}{0}}
delay = ${if >{$acl_m2}{0}{$acl_m2}{0}}s
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# This access control list is used for the HELO or EHLO command in
# an incoming SMTP transaction. The tests are run in order until the
# greeting is either accepted or denied.
acl_helo:
# Record the current timestamp, in order to calculate elapsed time
# for subsequent delays
warn
set acl_m2 = $tod_epoch
# Accept mail received over local SMTP (i.e. not over TCP/IP).
# We do this by testing for an empty sending host field.
# Also accept mails received from hosts for which we relay mail.
#
accept
hosts = : +relay_from_hosts
# If the remote host greets with an IP address, then prepare a reject
# message in $acl_c0, and a log message in $acl_c1. We will later use
# these in a "deny" statement. In the mean time, their presence indicate
# that we should keep stalling the sender.
#
warn
condition = ${if isip {$sender_helo_name}{true}{false}}
set acl_c0 = Message was delivered by ratware
set acl_c1 = remote host used IP address in HELO/EHLO greeting
# Likewise if the peer greets with one of our own names
#
warn
condition = ${if match_domain{$sender_helo_name}\
{$primary_hostname:+local_domains:+relay_to_domains}\
{true}{false}}
set acl_c0 = Message was delivered by ratware
set acl_c1 = remote host used our name in HELO/EHLO greeting.
# If HELO verification fails, we prepare a warning message in acl_c1.
# We will later add this message to the mail header. In the mean time,
# its presence indicates that we should keep stalling the sender.
#
warn
condition = ${if !def:acl_c1 {true}{false}}
!verify = helo
set acl_c1 = X-HELO-Warning: Remote host $sender_host_address \
${if def:sender_host_name {($sender_host_name) }}\
incorrectly presented itself as $sender_helo_name
log_message = remote host presented unverifiable HELO/EHLO greeting.
# Accept the greeting, but if we previously generated a message in
# $acl_c1, stall the sender until 20 seconds has elapsed.
accept
set acl_m2 = ${if def:acl_c1 {${eval:20 + $acl_m2 - $tod_epoch}}{0}}
delay = ${if >{$acl_m2}{0}{$acl_m2}{0}}s
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# This access control list is used for the MAIL FROM: command in an
# incoming SMTP transaction. The tests are run in order until the
# sender address is either accepted or denied.
#
acl_mail_from:
# Record the current timestamp, in order to calculate elapsed time
# for subsequent delays
warn
set acl_m2 = $tod_epoch
# Accept mail received over local SMTP (i.e. not over TCP/IP).
# We do this by testing for an empty sending host field.
# Also accept mails received from hosts for which we relay mail.
#
# Sender verification is omitted here, because in many cases
# the clients are dumb MUAs that don't cope well with SMTP
# error responses.
#
accept
hosts = : +relay_from_hosts
# Accept if the message arrived over an authenticated connection,
# from any host. Again, these messages are usually from MUAs.
#
accept
authenticated = *
# If present, the ACL variables $acl_c0 and $acl_c1 contain rejection
# and/or warning messages to be applied to every delivery attempt in
# in this SMTP transaction. Assign these to the corresponding
# $acl_m{0,1} message-specific variables, and add any warning message
# from $acl_m1 to the message header. (In the case of a rejection,
# $acl_m1 actually contains a log message instead, but this does not
# matter, as we will discard the header along with the message).
#
warn
set acl_m0 = $acl_c0
set acl_m1 = $acl_c1
message = $acl_c1
# If sender did not provide a HELO/EHLO greeting, then prepare a reject
# message in $acl_m0, and a log message in $acl_m1. We will later use
# these in a "deny" statement. In the mean time, their presence indicate
# that we should keep stalling the sender.
#
warn
condition = ${if def:sender_helo_name {0}{1}}
set acl_m0 = Message was delivered by ratware
set acl_m1 = remote host did not present HELO/EHLO greeting.
# If we could not verify the sender address, create a warning message
# in $acl_m1 and add it to the mail header. The presence of this
# message indicates that we should keep stalling the sender.
#
# You may choose to omit the "callout" option. In particular, if
# you are sending outgoing mail through a smarthost, it will not
# give any useful information.
#
warn
condition = ${if !def:acl_m1 {true}{false}}
!verify = sender/callout
set acl_m1 = Invalid sender <$sender_address>
message = X-Sender-Verify-Failed: $acl_m1
log_message = $acl_m1
# Accept the sender, but if we previously generated a message in
# $acl_c1, stall the sender until 20 seconds has elapsed.
accept
set acl_m2 = ${if def:acl_c1 {${eval:20 + $acl_m2 - $tod_epoch}}{0}}
delay = ${if >{$acl_m2}{0}{$acl_m2}{0}}s
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# This access control list is used for every RCPT command in an
# incoming SMTP message. The tests are run in order until the
# recipient address is either accepted or denied.
acl_rcpt_to:
# Accept mail received over local SMTP (i.e. not over TCP/IP).
# We do this by testing for an empty sending host field.
# Also accept mails received from hosts for which we relay mail.
#
# Recipient verification is omitted here, because in many
# cases the clients are dumb MUAs that don't cope well with
# SMTP error responses.
#
accept
hosts = : +relay_from_hosts
# Accept if the message arrived over an authenticated connection,
# from any host. Again, these messages are usually from MUAs, so
# recipient verification is omitted.
#
accept
authenticated = *
# Deny if the local part contains @ or % or / or | or !. These are
# rarely found in genuine local parts, but are often tried by people
# looking to circumvent relaying restrictions.
#
# Also deny if the local part starts with a dot. Empty components
# aren't strictly legal in RFC 2822, but Exim allows them because
# this is common. However, actually starting with a dot may cause
# trouble if the local part is used as a file name (e.g. for a
# mailing list).
#
deny
local_parts = ^.*[@%!/|] : ^\\.
# Deny if we have previously given a reason for doing so in $acl_m0.
# Also stall the sender for another 20s first.
#
deny
message = $acl_m0
log_message = $acl_m1
condition = ${if and {{def:acl_m0}{def:acl_m1}} {true}}
delay = 20s
# If the recipient address is not in a domain for which we are handling
# mail, stall the sender and reject.
#
deny
message = relay not permitted
!domains = +local_domains : +relay_to_domains
delay = 20s
# If the address is in a local domain or in a domain for which are
# relaying, but is invalid, stall and reject.
#
deny
message = unknown user
!verify = recipient/callout=20s,defer_ok,use_sender
delay = ${if def:sender_address {1m}{0s}}
# Drop the connection if the envelope sender is empty, but there is
# more than one recipient address. Legitimate DSNs are never sent
# to more than one address.
#
drop
message = Legitimate bounces are never sent to more than one \
recipient.
senders = : postmaster@*
condition = $recipients_count
delay = 5m
# --------------------------------------------------------------------
# Limit the number of recipients in each incoming message to one
# to support per-user settings and data (e.g. for SpamAssassin).
#
# NOTE: Every mail sent to several users at your site will be
# delayed for 30 minutes or more per recipient. This
# significantly slow down the pace of discussion threads
# involving several internal and external parties.
# Thus, it is commented out by default.
#
#defer
# message = We only accept one recipient at a time - please try later.
# condition = $recipients_count
# --------------------------------------------------------------------
# Accept the mail if the sending host is matched in the ".forwarders"
# file in the recipient's home directory. Temporarily set $acl_m9 to
# point to this file. If the host is found, set a flag in $acl_m0 and
# clear $acl_m1 to indicate that we should not reject this mail later.
#
accept
domains = +local_domains
set acl_m9 = /home/${extract{1}{=}{${lc:$local_part}}}/.forwarders
hosts = ${if exists {$acl_m9}{$acl_m9}}
set acl_m0 = accept
set acl_m1 =
# Accept the mail if the sending host is matched in the global
# whitelist file. Temporarily set $acl_m9 to point to this file.
# If the host is found, set a flag in $acl_m0 and clear $acl_m1 to
# indicate that we should not reject this mail later.
#
accept
set acl_m9 = /etc/mail/whitelist-hosts
hosts = ${if exists {$acl_m9}{$acl_m9}}
set acl_m0 = accept
set acl_m1 =
# --------------------------------------------------------------------
# Envelope Sender Signature Check.
# This is commented out by default, because it requires additional
# configuration in the 'transports' and 'routers' sections.
#
# Accept the recipient addresss if it contains our own signature.
# This means this is a response (DSN, sender callout verification...)
# to a message that was previously sent from here.
#
#accept
# domains = +local_domains
# condition = ${if and {{match{${lc:$local_part}}{^(.*)=(.*)}}\
# {eq{${hash_8:${hmac{md5}{SECRET}{$1}}}}{$2}}}\
# {true}{false}}
#
# Otherwise, if this message claims to be a bounce (i.e. if there
# is no envelope sender), but if the receiver has elected to use
# and check against envelope sender signatures, reject it.
#
#deny
# message = This address does not match a valid, signed \
# return path from here.\n\
# You are responding to a forged sender address.
# log_message = bogus bounce.
# senders = : postmaster@*
# domains = +local_domains
# set acl_m9 = /home/${extract{1}{=}{${lc:$local_part}}}/.return-path-sign
# condition = ${if exists {$acl_m9}{true}}
# --------------------------------------------------------------------
# --------------------------------------------------------------------
# Deny mail for local users that do not have a mailbox (i.e. postmaster,
# webmaster...) if no sender address is provided. These users do
# not send outgoing mail, so they should not receive returned mail.
#
# NOTE: This is commented out by default, because the condition is
# specific to how local mail is delivered. If you want to
# enable this check, uncomment one and only one of the
# conditions below.
#
#deny
# message = This address never sends outgoing mail. \
# You are responding to a forged sender address.
# log_message = bogus bounce for system user <$local_part@$domain>
# senders = : postmaster@*
# domains = +local_domains
# set acl_m9 = ${extract{1}{=}{${lc:$local_part}}}
#
# --- Uncomment the following 2 lines if recipients have local accounts:
# set acl_m9 = ${extract{2}{:}{${lookup passwd {$acl_m9}{$value}}}{0}}
# !condition = ${if and {{>={$acl_m9}{500}} {<${acl_m9}{60000}}} {true}}
#
# --- Uncomment the following line if you deliver mail to Cyrus:
# condition = ${run {/usr/sbin/mbpath -q -s user.$acl_m9} {true}}
# --------------------------------------------------------------------
# Query the SPF information for the sender address domain, if any,
# to see if the sending host is authorized to deliver its mail.
# If not, reject the mail.
#
deny
message = [SPF] $sender_host_address is not allowed to send mail \
from $sender_address_domain
log_message = SPF check failed.
spf = fail
# Add a SPF-Received: line to the message header
warn
message = $spf_received
# --------------------------------------------------------------------
# Check greylisting status for this particular peer/sender/recipient.
# Before uncommenting this statement, you need to install "greylistd".
# See: http://packages.debian.org/unstable/main/greylistd
#
# Note that we do not greylist messages with NULL sender, because
# sender callout verification would break (and we might not be able
# to send mail to a host that performs callouts).
#
#defer
# message = $sender_host_address is not yet authorized to deliver mail \
# from <$sender_address> to <$local_part@$domain>. \
# Please try later.
# log_message = greylisted.
# domains = +local_domains : +relay_to_domains
# !senders = : postmaster@*
# set acl_m9 = $sender_host_address $sender_address $local_part@$domain
# set acl_m9 = ${readsocket{/var/run/greylistd/socket}{$acl_m9}{5s}{}{}}
# condition = ${if eq {$acl_m9}{grey}{true}{false}}
# delay = 20s
# --------------------------------------------------------------------
# Accept the recipient.
accept
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# This access control list is used for message data received via
# SMTP. The tests are run in order until the recipient address
# is either accepted or denied.
acl_data:
# Log some header lines
warn
logwrite = Subject: $h_Subject:
# Add Message-ID if missing in messages received from our own hosts.
warn
condition = ${if !def:h_Message-ID: {1}}
hosts = +relay_from_hosts
message = Message-ID: <E$message_id@$primary_hostname>
# Accept mail received over local SMTP (i.e. not over TCP/IP).
# We do this by testing for an empty sending host field.
# Also accept mails received from hosts for which we relay mail.
#
accept
hosts = : +relay_from_hosts
# Accept if the message arrived over an authenticated connection, from
# any host.
#
accept
authenticated = *
# Deny if we have previously given a reason for doing so in $acl_m0.
# Also stall the sender for another 20s first.
#
deny
message = $acl_m0
log_message = $acl_m1
condition = ${if and {{def:acl_m0}{def:acl_m1}} {true}{false}}
delay = 20s
# enforce a message-size limit
#
deny
message = Message size $message_size is larger than limit of \
MESSAGE_SIZE_LIMIT
condition = ${if >{$message_size}{MESSAGE_SIZE_LIMIT}{yes}{no}}
# Deny unless the addresses in the header is syntactically correct.
#
deny
message = Your message does not conform to RFC2822 standard
log_message = message header fail syntax check
!verify = header_syntax
# Uncomment the following to deny non-local messages without
# a Message-ID:, Date:, or Subject: header.
#
# Note that some specialized MTAs, such as certain mailing list
# servers, do not automatically generate a Message-ID for bounces.
# Thus, we add the check for a non-empty sender.
#
#deny
# message = Your message does not conform to RFC2822 standard
# log_message = missing header lines
# !hosts = +relay_from_hosts
# !senders = : postmaster@*
# condition = ${if !eq {$acl_m0}{accept}{true}}
# condition = ${if or {{!def:h_Message-ID:}\
# {!def:h_Date:}\
# {!def:h_Subject:}} {true}{false}}
# Warn unless there is a verifiable sender address in at least
# one of the "Sender:", "Reply-To:", or "From:" header lines.
#
warn
message = X-Sender-Verify-Failed: No valid sender in message header
log_message = No valid sender in message header
!verify = header_sender
# --------------------------------------------------------------------
# Perform greylisting on messages with no envelope sender here.
# We did not subject these to greylisting after RCPT TO: because
# that would interfere with remote hosts doing sender callouts.
# Note that the sender address is empty, so we don't bother using it.
#
# Before uncommenting this statement, you need to install "greylistd".
# See: http://packages.debian.org/unstable/main/greylistd
#
#defer
# message = $sender_host_address is not yet authorized to send \
# delivery status reports to <$recipients>. \
# Please try later.
# log_message = greylisted.
# senders = : postmaster@*
# condition = ${if !eq {$acl_m0}{accept}{true}}
# set acl_m9 = $sender_host_address $recipients
# set acl_m9 = ${readsocket{/var/run/greylistd/socket}{$acl_m9}{5s}{}{}}
# condition = ${if eq {$acl_m9}{grey}{true}{false}}
# delay = 20s
# --------------------------------------------------------------------
# --- BEGIN EXISCAN configuration ---
# Reject messages that have serious MIME errors.
#
deny
message = Serious MIME defect detected ($demime_reason)
demime = *
condition = ${if >{$demime_errorlevel}{2}{1}{0}}
# Unpack MIME containers and reject file extensions used by worms.
# This calls the demime condition again, but it will return cached results.
# Note that the extension list may be incomplete.
#
deny
message = We do not accept ".$found_extension" attachments here.
demime = bat:btm:cmd:com:cpl:dll:exe:lnk:msi:pif:prf:reg:scr:vbs:url
# Messages larger than MESSAGE_SIZE_SPAM_MAX are accepted without
# spam or virus scanning
accept
condition = ${if >{$message_size}{MESSAGE_SIZE_SPAM_MAX} {true}}
logwrite = :main: Not classified \
(message size larger than MESSAGE_SIZE_SPAM_MAX)
# --------------------------------------------------------------------
# Anti-Virus scanning
# This requires an 'av_scanner' setting in the main section.
#
#deny
# message = This message contains a virus ($malware_name)
# demime = *
# malware = */defer_ok
# --------------------------------------------------------------------
# Invoke SpamAssassin to obtain $spam_score and $spam_report.
# Depending on the classification, $acl_m9 is set to "ham" or "spam".
#
# If the message is classified as spam, and we have not previously
# set $acl_m0 to indicate that we want to accept it anyway, pretend
# reject it.
#
warn
set acl_m9 = ham
# ------------------------------------------------------------------
# If you want to allow per-user settings for SpamAssassin,
# uncomment the following line, and comment out "spam = mail".
# We pass on the username specified in the recipient address,
# i.e. the portion before any '=' or '@' character, converted
# to lowercase. Multiple recipients should not occur, since
# we previously limited delivery to one recipient at a time.
#
# spam = ${lc:${extract{1}{=@}{$recipients}{$value}{mail}}}
# ------------------------------------------------------------------
spam = mail
set acl_m9 = spam
condition = ${if !eq {$acl_m0}{accept}{true}}
control = fakereject
logwrite = :reject: Rejected spam (score $spam_score): $spam_report
# Add an appropriate X-Spam-Status: header to the message.
#
warn
message = X-Spam-Status: \
${if eq {$acl_m9}{spam}{Yes}{No}} (score $spam_score)\
${if def:spam_report {: $spam_report}}
logwrite = :main: Classified as $acl_m9 (score $spam_score)
# --- END EXISCAN configuration ---
# Accept the message.
#
accept
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