path: root/debian/debconf/conf.d/acl/30_exim4-config_check_rcpt

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

# define macros to be used below in this file to check recipient
# local parts for strange characters. Documentation below.
# This blocks local parts that begin with a dot or contain a quite
# broad range of non-alphanumeric characters.

.ifndef CHECK_RCPT_LOCAL_LOCALPARTS
CHECK_RCPT_LOCAL_LOCALPARTS = ^[.] : ^.*[@%!/|`#&?]
.endif

.ifndef CHECK_RCPT_REMOTE_LOCALPARTS
CHECK_RCPT_REMOTE_LOCALPARTS = ^[./|] : ^.*[@%!`#&?] : ^.*/\\.\\./
.endif

# 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

  # Do not try to verify DKIM signatures of incoming mail if DC_minimaldns
  # or DISABLE_DKIM_VERIFY are set.
.ifdef DC_minimaldns
  warn
    control = dkim_disable_verify
.else
.ifdef DISABLE_DKIM_VERIFY
  warn
    control = dkim_disable_verify
.endif
.endif

  # 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 RFC5322 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
  # at the top of this file.
  .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 section
  # "Access control lists" subsection "Address verification" with the added
  # information that a smarthost/satellite setup routes all non-local e-mail
  # to the smarthost.
  .ifdef CHECK_RCPT_VERIFY_SENDER
  deny
    !acl = acl_local_deny_exceptions
    !verify = sender
    message = Sender verification failed
  .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_local_deny_exceptions
    senders = ${if exists{CONFDIR/local_sender_callout}\
                         {CONFDIR/local_sender_callout}\
                   {}}
    !verify = sender/callout

  .ifndef CHECK_RCPT_NO_FAIL_TOO_MANY_BAD_RCPT
  # Reject all RCPT commands after too many bad recipients
  # This is partly a defense against spam abuse and partly attacker abuse.
  # Real senders should manage, by the time they get to 10 RCPT directives,
  # to have had at least half of them be real addresses.
  #
  # This is a lightweight check and can protect you against repeated
  # invocations of more heavy-weight checks which would come after it.

  deny    condition     = ${if and {\
                        {>{$rcpt_count}{10}}\
                        {<{$recipients_count}{${eval:$rcpt_count/2}}} }}
          message       = Rejected for too many bad recipients
          logwrite      = REJECT [$sender_host_address]: bad recipient count high [${eval:$rcpt_count-$recipients_count}]
  .endif

  # 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
    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/sender_retain
    control = dkim_disable_verify

  # 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_local_deny_exceptions
    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
    !acl = acl_local_deny_exceptions
    senders = ${if exists{CONFDIR/local_sender_blacklist}\
                   {CONFDIR/local_sender_blacklist}\
                   {}}
    message = sender envelope address $sender_address is locally blacklisted here. If you think this is wrong, get in touch with postmaster
    log_message = sender envelope address is locally blacklisted.


  # 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 exim4-config_files(5) for details.
  deny
    !acl = acl_local_deny_exceptions
    hosts = ${if exists{CONFDIR/local_host_blacklist}\
                 {CONFDIR/local_host_blacklist}\
                 {}}
    message = sender IP address $sender_host_address is locally blacklisted here. If you think this is wrong, get in touch with postmaster
    log_message = sender IP address is locally blacklisted.


  # 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
    condition = ${if and{{def:sender_host_address}{!def:sender_host_name}}\
                      {yes}{no}}
    add_header = X-Host-Lookup-Failed: Reverse DNS lookup failed for $sender_host_address (${if eq{$host_lookup_failed}{1}{failed}{deferred}})
  .endif


  .ifdef CHECK_RCPT_SPF
  .ifdef _HAVE_SPF
  deny
    !acl = acl_local_deny_exceptions
    spf = fail
    message = [SPF] $sender_host_address is not allowed to send mail from \
              ${if def:sender_address_domain {$sender_address_domain}{$sender_helo_name}}.
    log_message = SPF check failed.

  defer
    !acl = acl_local_deny_exceptions
    spf = temperror
    message = Temporary DNS error while checking SPF record.  Try again later.

  warn
    spf = pass:softfail:neutral:permerror
    add_header = :at_start:$spf_received
  .endif
  .endif


  # Check against classic DNS "black" lists (DNSBLs) which list
  # sender IP addresses
  .ifdef CHECK_RCPT_IP_DNSBLS
  warn
    dnslists = CHECK_RCPT_IP_DNSBLS
    add_header = 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)
  .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
    !senders = ${if exists{CONFDIR/local_domain_dnsbl_whitelist}\
                    {CONFDIR/local_domain_dnsbl_whitelist}\
                    {}}
    dnslists = CHECK_RCPT_DOMAIN_DNSBLS
    add_header = 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)
  .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