30_exim4-config_check_rcpt

exim4+conf.d

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### acl/30_exim4-config_check_rcpt
################################# 

# 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 = :


 # The following section of the ACL is concerned with local parts that contain
 # certain non-alphanumeric characters. Dots in unusual places are
 # handled by this ACL as well.
 #
 # Non-alphanumeric 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 disallow certain non-alphanumeric characters, 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
 # a name without a 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.
 #
 # These ACL components will block recipient addresses that are valid
 # from an RFC2822 point of view. We chose to have them blocked by
 # default for security reasons.
 #
 # If you feel that your site should have less strict recipient
 # checking, please feel free to change the default values of the macros
 # defined in main/01_exim4-config_listmacrosdefs or override them from a
 # local configuration file.
 # 
 # Two different rules are used. The first one has a quite strict
 # default, and is applied to messages that are addressed to one of the
 # local domains handled by this host.

 # The default value of CHECK_RCPT_LOCAL_LOCALPARTS is defined in
 # main/01_exim4-config_listmacrosdefs:
 # CHECK_RCPT_LOCAL_LOCALPARTS = ^[.] : ^.*[@%!/|`#&?]
 # This blocks local parts that begin with a dot or contain a quite
 # broad range of non-alphanumeric characters.
 .ifdef CHECK_RCPT_LOCAL_LOCALPARTS
 deny
   domains = +local_domains
   local_parts = CHECK_RCPT_LOCAL_LOCALPARTS
   message = restricted characters in address
 .endif


 # The second rule applies to all other domains, and its default is
 # considerably less strict.
 
 # The default value of CHECK_RCPT_REMOTE_LOCALPARTS is defined in
 # main/01_exim4-config_listmacrosdefs:
 # CHECK_RCPT_REMOTE_LOCALPARTS = ^[./|] : ^.*[@%!`#&?] : ^.*/\\.\\./

 # It allows local 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 some other non-alphanumeric characters is blocked.
 # Single quotes might probably be dangerous as well, but they're
 # allowed by the default regexps to avoid rejecting mails to Ireland.
 # The motivation here is to prevent local users (or local users' malware)
 # from mounting certain kinds of attack on remote sites.
 .ifdef CHECK_RCPT_REMOTE_LOCALPARTS
 deny
   domains = !+local_domains
   local_parts = CHECK_RCPT_REMOTE_LOCALPARTS
   message = restricted characters in address
 .endif


 # Accept mail to postmaster in any local domain, regardless of the source,
 # and without verifying the sender.
 #
 accept
   .ifndef CHECK_RCPT_POSTMASTER
   local_parts = postmaster
   .else
   local_parts = CHECK_RCPT_POSTMASTER
   .endif
   domains = +local_domains : +relay_to_domains


 # Deny unless the sender address can be verified.
 #
 # This is disabled by default so that DNSless systems don't break. If
 # your system can do DNS lookups without delay or cost, you might want
 # to enable this feature.
 #
 # This feature does not work in smarthost and satellite setups as
 # with these setups all domains pass verification. See spec.txt chapter
 # 39.31 with the added information that a smarthost/satellite setup
 # routes all non-local e-mail to the smarthost.
 .ifdef CHECK_RCPT_VERIFY_SENDER
 deny
   message = Sender verification failed
   !acl = acl_whitelist_local_deny
   !verify = sender
 .endif

 # Verify senders listed in local_sender_callout with a callout.
 #
 # In smarthost and satellite setups, this causes the callout to be
 # done to the smarthost. Verification will thus only be reliable if the
 # smarthost does reject illegal addresses in the SMTP dialog.
 deny
   !acl = acl_whitelist_local_deny
   senders = ${if exists{CONFDIR/local_sender_callout}\
                        {CONFDIR/local_sender_callout}\
                  {}}
   !verify = sender/callout


 # 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 black
 # list, it is a mistake.
 accept
   hosts = +relay_from_hosts
   control = submission/sender_retain


 # 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/sender_retain


 # 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.
 require
   verify = recipient


 # Verify recipients listed in local_rcpt_callout with a callout.
 # This is especially handy for forwarding MX hosts (secondary MX or
 # mail hubs) of domains that receive a lot of spam to non-existent
 # addresses.  The only way to check local parts for remote relay
 # domains is to use a callout (add /callout), but please read the
 # documentation about callouts before doing this.
 deny
   !acl = acl_whitelist_local_deny
   recipients = ${if exists{CONFDIR/local_rcpt_callout}\
                           {CONFDIR/local_rcpt_callout}\
                     {}}
   !verify = recipient/callout


 # CONFDIR/local_sender_blacklist holds a list of envelope senders that
 # should have their access denied to the local host. Incoming messages
 # with one of these senders are rejected at RCPT time.
 #
 # The explicit white lists are honored as well as negative items in
 # the black list. See exim4-config_files(5) for details.
 deny
   message = sender envelope address $sender_address is locally blacklisted here. If you think this is wrong, get in touch with postmaster
   !acl = acl_whitelist_local_deny
   senders = ${if exists{CONFDIR/local_sender_blacklist}\
                  {CONFDIR/local_sender_blacklist}\
                  {}}


 # deny bad sites (IP address)
 # CONFDIR/local_host_blacklist holds a list of host names, IP addresses
 # and networks (CIDR notation)  that should have their access denied to
 # The local host. Messages coming in from a listed host will have all
 # RCPT statements rejected.
 #
 # The explicit white lists are honored as well as negative items in
 # the black list. See /usr/share/doc/exim4-config/default_acl for details.
 deny
   message = sender IP address $sender_host_address is locally blacklisted here. If you think this is wrong, get in touch with postmaster
   !acl = acl_whitelist_local_deny
   hosts = ${if exists{CONFDIR/local_host_blacklist}\
                {CONFDIR/local_host_blacklist}\
                {}}


 # Warn if the sender host does not have valid reverse DNS.
 # 
 # If your system can do DNS lookups without delay or cost, you might want
 # to enable this.
 # If sender_host_address is defined, it's a remote call.  If
 # sender_host_name is not defined, then reverse lookup failed.  Use
 # this instead of !verify = reverse_host_lookup to catch deferrals
 # as well as outright failures.
 .ifdef CHECK_RCPT_REVERSE_DNS
 warn
   message = X-Host-Lookup-Failed: Reverse DNS lookup failed for $sender_host_address (${if eq{$host_lookup_failed}{1}{failed}{deferred}})
    condition = ${if and{{def:sender_host_address}{!def:sender_host_name}}\
                     {yes}{no}}
 .endif


 # Use spfquery to perform a pair of SPF checks (for details, see
 # http://www.openspf.org/)
 #
 # This is quite costly in terms of DNS lookups (~6 lookups per mail).  Do not
 # enable if that's an issue.  Also note that if you enable this, you must
 # install "libmail-spf-query-perl" which provides the spfquery command.
 # Missing libmail-spf-query-perl will trigger the "Unexpected error in
 # SPF check" warning.
 .ifdef CHECK_RCPT_SPF
 deny
   message = [SPF] $sender_host_address is not allowed to send mail from ${if def:sender_address_domain {$sender_address_domain}{$sender_helo_name}}.  \
             Please see http://www.openspf.org/why.html?sender=$sender_address&ip=$sender_host_address
   log_message = SPF check failed.
   condition = ${run{/usr/bin/spfquery --ip \"$sender_host_address\" --mail-from \"$sender_address\" --helo \"$sender_helo_name\"}\
                    {no}{${if eq {$runrc}{1}{yes}{no}}}}

 defer
   message = Temporary DNS error while checking SPF record.  Try again later.
   condition = ${if eq {$runrc}{5}{yes}{no}}

 warn
   message = Received-SPF: ${if eq {$runrc}{0}{pass}{${if eq {$runrc}{2}{softfail}\
                                {${if eq {$runrc}{3}{neutral}{${if eq {$runrc}{4}{unknown}{${if eq {$runrc}{6}{none}{error}}}}}}}}}}
   condition = ${if <={$runrc}{6}{yes}{no}}

 warn
   log_message = Unexpected error in SPF check.
   condition = ${if >{$runrc}{6}{yes}{no}}

 # Support for best-guess (see http://www.openspf.org/developers-guide.html)
 warn
   message = X-SPF-Guess: ${run{/usr/bin/spfquery --ip \"$sender_host_address\"  --mail-from \"$sender_address\" \ --helo \"$sender_helo_name\" --guess true}\
                               {pass}{${if eq {$runrc}{2}{softfail}{${if eq {$runrc}{3}{neutral}{${if eq {$runrc}{4}{unknown}\
                               {${if eq {$runrc}{6}{none}{error}}}}}}}}}}
   condition = ${if <={$runrc}{6}{yes}{no}}

 defer
   message = Temporary DNS error while checking SPF record.  Try again later.
   condition = ${if eq {$runrc}{5}{yes}{no}}
 .endif


 # Check against classic DNS "black" lists (DNSBLs) which list
 # sender IP addresses
 .ifdef CHECK_RCPT_IP_DNSBLS
 warn
   message = X-Warning: $sender_host_address is listed at $dnslist_domain ($dnslist_value: $dnslist_text)
   log_message = $sender_host_address is listed at $dnslist_domain ($dnslist_value: $dnslist_text)
   dnslists = CHECK_RCPT_IP_DNSBLS
 .endif


 # Check against DNSBLs which list sender domains, with an option to locally
 # whitelist certain domains that might be blacklisted.
 #
 # Note: If you define CHECK_RCPT_DOMAIN_DNSBLS, you must append
 # "/$sender_address_domain" after each domain.  For example:
 # CHECK_RCPT_DOMAIN_DNSBLS = rhsbl.foo.org/$sender_address_domain \
 #                            : rhsbl.bar.org/$sender_address_domain
 .ifdef CHECK_RCPT_DOMAIN_DNSBLS
 warn
   message = X-Warning: $sender_address_domain is listed at $dnslist_domain ($dnslist_value: $dnslist_text)
   log_message = $sender_address_domain is listed at $dnslist_domain ($dnslist_value: $dnslist_text)
   !senders = ${if exists{CONFDIR/local_domain_dnsbl_whitelist}\
                   {CONFDIR/local_domain_dnsbl_whitelist}\
                   {}}
   dnslists = CHECK_RCPT_DOMAIN_DNSBLS
 .endif


 # This hook allows you to hook in your own ACLs without having to
 # modify this file. If you do it like we suggest, you'll end up with
 # a small performance penalty since there is an additional file being
 # accessed. This doesn't happen if you leave the macro unset.
 .ifdef CHECK_RCPT_LOCAL_ACL_FILE
 .include CHECK_RCPT_LOCAL_ACL_FILE
 .endif


 #############################################################################
 # 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
 #############################################################################


 # Accept if the address is in a domain for which we are an incoming relay,
 # but again, only if the recipient can be verified.

 accept
   domains = +relay_to_domains
   endpass
   verify = recipient


 # At this point, the address has passed all the checks that have been
 # configured, so we accept it unconditionally.

 accept