debian/debconf/conf.d/acl/30_exim4-config_check_rcpt

   1
   2 ### acl/30_exim4-config_check_rcpt
   3 #################################
   4
   5 # This access control list is used for every RCPT command in an incoming
   6 # SMTP message. The tests are run in order until the address is either
   7 # accepted or denied.
   8 #
   9 acl_check_rcpt:
  10
  11   # Accept if the source is local SMTP (i.e. not over TCP/IP). We do this by
  12   # testing for an empty sending host field.
  13   accept
  14     hosts = :
  15     control = dkim_disable_verify
  16
  17   # Do not try to verify DKIM signatures of incoming mail if DC_minimaldns
  18   # or DISABLE_DKIM_VERIFY are set.
  19 .ifdef DC_minimaldns
  20   warn
  21     control = dkim_disable_verify
  22 .else
  23 .ifdef DISABLE_DKIM_VERIFY
  24   warn
  25     control = dkim_disable_verify
  26 .endif
  27 .endif
  28
  29   # The following section of the ACL is concerned with local parts that contain
  30   # certain non-alphanumeric characters. Dots in unusual places are
  31   # handled by this ACL as well.
  32   #
  33   # Non-alphanumeric characters other than dots are rarely found in genuine
  34   # local parts, but are often tried by people looking to circumvent
  35   # relaying restrictions. Therefore, although they are valid in local
  36   # parts, these rules disallow certain non-alphanumeric characters, as
  37   # a precaution.
  38   #
  39   # Empty components (two dots in a row) are not valid in RFC 2822, but Exim
  40   # allows them because they have been encountered. (Consider local parts
  41   # constructed as "firstinitial.secondinitial.familyname" when applied to
  42   # a name without a second initial.) However, a local part starting
  43   # with a dot or containing /../ can cause trouble if it is used as part of a
  44   # file name (e.g. for a mailing list). This is also true for local parts that
  45   # contain slashes. A pipe symbol can also be troublesome if the local part is
  46   # incorporated unthinkingly into a shell command line.
  47   #
  48   # These ACL components will block recipient addresses that are valid
  49   # from an RFC2822 point of view. We chose to have them blocked by
  50   # default for security reasons.
  51   #
  52   # If you feel that your site should have less strict recipient
  53   # checking, please feel free to change the default values of the macros
  54   # defined in main/01_exim4-config_listmacrosdefs or override them from a
  55   # local configuration file.
  56   #
  57   # Two different rules are used. The first one has a quite strict
  58   # default, and is applied to messages that are addressed to one of the
  59   # local domains handled by this host.
  60
  61   # The default value of CHECK_RCPT_LOCAL_LOCALPARTS is defined in
  62   # main/01_exim4-config_listmacrosdefs:
  63   # CHECK_RCPT_LOCAL_LOCALPARTS = ^[.] : ^.*[@%!/|`#&?]
  64   # This blocks local parts that begin with a dot or contain a quite
  65   # broad range of non-alphanumeric characters.
  66   .ifdef CHECK_RCPT_LOCAL_LOCALPARTS
  67   deny
  68     domains = +local_domains
  69     local_parts = CHECK_RCPT_LOCAL_LOCALPARTS
  70     message = restricted characters in address
  71   .endif
  72
  73
  74   # The second rule applies to all other domains, and its default is
  75   # considerably less strict.
  76
  77   # The default value of CHECK_RCPT_REMOTE_LOCALPARTS is defined in
  78   # main/01_exim4-config_listmacrosdefs:
  79   # CHECK_RCPT_REMOTE_LOCALPARTS = ^[./|] : ^.*[@%!`#&?] : ^.*/\\.\\./
  80
  81   # It allows local users to send outgoing messages to sites
  82   # that use slashes and vertical bars in their local parts. It blocks
  83   # local parts that begin with a dot, slash, or vertical bar, but allows
  84   # these characters within the local part. However, the sequence /../ is
  85   # barred. The use of some other non-alphanumeric characters is blocked.
  86   # Single quotes might probably be dangerous as well, but they're
  87   # allowed by the default regexps to avoid rejecting mails to Ireland.
  88   # The motivation here is to prevent local users (or local users' malware)
  89   # from mounting certain kinds of attack on remote sites.
  90   .ifdef CHECK_RCPT_REMOTE_LOCALPARTS
  91   deny
  92     domains = !+local_domains
  93     local_parts = CHECK_RCPT_REMOTE_LOCALPARTS
  94     message = restricted characters in address
  95   .endif
  96
  97
  98   # Accept mail to postmaster in any local domain, regardless of the source,
  99   # and without verifying the sender.
 100   #
 101   accept
 102     .ifndef CHECK_RCPT_POSTMASTER
 103     local_parts = postmaster
 104     .else
 105     local_parts = CHECK_RCPT_POSTMASTER
 106     .endif
 107     domains = +local_domains : +relay_to_domains
 108
 109
 110   # Deny unless the sender address can be verified.
 111   #
 112   # This is disabled by default so that DNSless systems don't break. If
 113   # your system can do DNS lookups without delay or cost, you might want
 114   # to enable this feature.
 115   #
 116   # This feature does not work in smarthost and satellite setups as
 117   # with these setups all domains pass verification. See spec.txt chapter
 118   # 39.31 with the added information that a smarthost/satellite setup
 119   # routes all non-local e-mail to the smarthost.
 120   .ifdef CHECK_RCPT_VERIFY_SENDER
 121   deny
 122     message = Sender verification failed
 123     !acl = acl_local_deny_exceptions
 124     !verify = sender
 125   .endif
 126
 127   # Verify senders listed in local_sender_callout with a callout.
 128   #
 129   # In smarthost and satellite setups, this causes the callout to be
 130   # done to the smarthost. Verification will thus only be reliable if the
 131   # smarthost does reject illegal addresses in the SMTP dialog.
 132   deny
 133     !acl = acl_local_deny_exceptions
 134     senders = ${if exists{CONFDIR/local_sender_callout}\
 135                          {CONFDIR/local_sender_callout}\
 136                    {}}
 137     !verify = sender/callout
 138
 139
 140   # Accept if the message comes from one of the hosts for which we are an
 141   # outgoing relay. It is assumed that such hosts are most likely to be MUAs,
 142   # so we set control=submission to make Exim treat the message as a
 143   # submission. It will fix up various errors in the message, for example, the
 144   # lack of a Date: header line. If you are actually relaying out out from
 145   # MTAs, you may want to disable this. If you are handling both relaying from
 146   # MTAs and submissions from MUAs you should probably split them into two
 147   # lists, and handle them differently.
 148
 149   # Recipient verification is omitted here, because in many cases the clients
 150   # are dumb MUAs that don't cope well with SMTP error responses. If you are
 151   # actually relaying out from MTAs, you should probably add recipient
 152   # verification here.
 153
 154   # Note that, by putting this test before any DNS black list checks, you will
 155   # always accept from these hosts, even if they end up on a black list. The
 156   # assumption is that they are your friends, and if they get onto black
 157   # list, it is a mistake.
 158   accept
 159     hosts = +relay_from_hosts
 160     control = submission/sender_retain
 161     control = dkim_disable_verify
 162
 163
 164   # Accept if the message arrived over an authenticated connection, from
 165   # any host. Again, these messages are usually from MUAs, so recipient
 166   # verification is omitted, and submission mode is set. And again, we do this
 167   # check before any black list tests.
 168   accept
 169     authenticated = *
 170     control = submission/sender_retain
 171     control = dkim_disable_verify
 172
 173
 174   # Insist that any other recipient address that we accept is either in one of
 175   # our local domains, or is in a domain for which we explicitly allow
 176   # relaying. Any other domain is rejected as being unacceptable for relaying.
 177   require
 178     message = relay not permitted
 179     domains = +local_domains : +relay_to_domains
 180
 181
 182   # We also require all accepted addresses to be verifiable. This check will
 183   # do local part verification for local domains, but only check the domain
 184   # for remote domains.
 185   require
 186     verify = recipient
 187
 188
 189   # Verify recipients listed in local_rcpt_callout with a callout.
 190   # This is especially handy for forwarding MX hosts (secondary MX or
 191   # mail hubs) of domains that receive a lot of spam to non-existent
 192   # addresses.  The only way to check local parts for remote relay
 193   # domains is to use a callout (add /callout), but please read the
 194   # documentation about callouts before doing this.
 195   deny
 196     !acl = acl_local_deny_exceptions
 197     recipients = ${if exists{CONFDIR/local_rcpt_callout}\
 198                             {CONFDIR/local_rcpt_callout}\
 199                       {}}
 200     !verify = recipient/callout
 201
 202
 203   # CONFDIR/local_sender_blacklist holds a list of envelope senders that
 204   # should have their access denied to the local host. Incoming messages
 205   # with one of these senders are rejected at RCPT time.
 206   #
 207   # The explicit white lists are honored as well as negative items in
 208   # the black list. See exim4-config_files(5) for details.
 209   deny
 210     message = sender envelope address $sender_address is locally blacklisted here. If you think this is wrong, get in touch with postmaster
 211     !acl = acl_local_deny_exceptions
 212     senders = ${if exists{CONFDIR/local_sender_blacklist}\
 213                    {CONFDIR/local_sender_blacklist}\
 214                    {}}
 215
 216
 217   # deny bad sites (IP address)
 218   # CONFDIR/local_host_blacklist holds a list of host names, IP addresses
 219   # and networks (CIDR notation)  that should have their access denied to
 220   # The local host. Messages coming in from a listed host will have all
 221   # RCPT statements rejected.
 222   #
 223   # The explicit white lists are honored as well as negative items in
 224   # the black list. See exim4-config_files(5) for details.
 225   deny
 226     message = sender IP address $sender_host_address is locally blacklisted here. If you think this is wrong, get in touch with postmaster
 227     !acl = acl_local_deny_exceptions
 228     hosts = ${if exists{CONFDIR/local_host_blacklist}\
 229                  {CONFDIR/local_host_blacklist}\
 230                  {}}
 231
 232
 233   # Warn if the sender host does not have valid reverse DNS.
 234   #
 235   # If your system can do DNS lookups without delay or cost, you might want
 236   # to enable this.
 237   # If sender_host_address is defined, it's a remote call.  If
 238   # sender_host_name is not defined, then reverse lookup failed.  Use
 239   # this instead of !verify = reverse_host_lookup to catch deferrals
 240   # as well as outright failures.
 241   .ifdef CHECK_RCPT_REVERSE_DNS
 242   warn
 243     condition = ${if and{{def:sender_host_address}{!def:sender_host_name}}\
 244                       {yes}{no}}
 245     add_header = X-Host-Lookup-Failed: Reverse DNS lookup failed for $sender_host_address (${if eq{$host_lookup_failed}{1}{failed}{deferred}})
 246   .endif
 247
 248
 249   # Use spfquery to perform a pair of SPF checks (for details, see
 250   # http://www.openspf.org/)
 251   #
 252   # This is quite costly in terms of DNS lookups (~6 lookups per mail).  Do not
 253   # enable if that's an issue.  Also note that if you enable this, you must
 254   # install "spf-tools-perl" which provides the spfquery command.
 255   # Missing spf-tools-perl will trigger the "Unexpected error in
 256   # SPF check" warning.
 257   .ifdef CHECK_RCPT_SPF
 258   deny
 259     message = [SPF] $sender_host_address is not allowed to send mail from \
 260               ${if def:sender_address_domain {$sender_address_domain}{$sender_helo_name}}.  \
 261               Please see \
 262               http://www.openspf.org/Why?scope=${if def:sender_address_domain \
 263               {mfrom}{helo}};identity=${if def:sender_address_domain \
 264               {$sender_address}{$sender_helo_name}};ip=$sender_host_address
 265     log_message = SPF check failed.
 266     !acl = acl_local_deny_exceptions
 267     condition = ${run{/usr/bin/spfquery.mail-spf-perl --ip \
 268                    ${quote:$sender_host_address} --identity \
 269                    ${if def:sender_address_domain \
 270                        {--scope mfrom  --identity ${quote:$sender_address}}\
 271                        {--scope helo --identity ${quote:$sender_helo_name}}}}\
 272                    {no}{${if eq {$runrc}{1}{yes}{no}}}}
 273
 274   defer
 275     message = Temporary DNS error while checking SPF record.  Try again later.
 276     !acl = acl_local_deny_exceptions
 277     condition = ${if eq {$runrc}{5}{yes}{no}}
 278
 279   warn
 280     condition = ${if <={$runrc}{6}{yes}{no}}
 281     add_header = Received-SPF: ${if eq {$runrc}{0}{pass}\
 282                                 {${if eq {$runrc}{2}{softfail}\
 283                                  {${if eq {$runrc}{3}{neutral}\
 284                                   {${if eq {$runrc}{4}{permerror}\
 285                                    {${if eq {$runrc}{6}{none}{error}}}}}}}}}\
 286                                 } client-ip=$sender_host_address; \
 287                                 ${if def:sender_address_domain \
 288                                    {envelope-from=${sender_address}; }{}}\
 289                                 helo=$sender_helo_name
 290
 291   warn
 292     log_message = Unexpected error in SPF check.
 293     condition = ${if >{$runrc}{6}{yes}{no}}
 294   .endif
 295
 296
 297   # Check against classic DNS "black" lists (DNSBLs) which list
 298   # sender IP addresses
 299   .ifdef CHECK_RCPT_IP_DNSBLS
 300   warn
 301     dnslists = CHECK_RCPT_IP_DNSBLS
 302     add_header = X-Warning: $sender_host_address is listed at $dnslist_domain ($dnslist_value: $dnslist_text)
 303     log_message = $sender_host_address is listed at $dnslist_domain ($dnslist_value: $dnslist_text)
 304   .endif
 305
 306
 307   # Check against DNSBLs which list sender domains, with an option to locally
 308   # whitelist certain domains that might be blacklisted.
 309   #
 310   # Note: If you define CHECK_RCPT_DOMAIN_DNSBLS, you must append
 311   # "/$sender_address_domain" after each domain.  For example:
 312   # CHECK_RCPT_DOMAIN_DNSBLS = rhsbl.foo.org/$sender_address_domain \
 313   #                            : rhsbl.bar.org/$sender_address_domain
 314   .ifdef CHECK_RCPT_DOMAIN_DNSBLS
 315   warn
 316     !senders = ${if exists{CONFDIR/local_domain_dnsbl_whitelist}\
 317                     {CONFDIR/local_domain_dnsbl_whitelist}\
 318                     {}}
 319     dnslists = CHECK_RCPT_DOMAIN_DNSBLS
 320     add_header = X-Warning: $sender_address_domain is listed at $dnslist_domain ($dnslist_value: $dnslist_text)
 321     log_message = $sender_address_domain is listed at $dnslist_domain ($dnslist_value: $dnslist_text)
 322   .endif
 323
 324
 325   # This hook allows you to hook in your own ACLs without having to
 326   # modify this file. If you do it like we suggest, you'll end up with
 327   # a small performance penalty since there is an additional file being
 328   # accessed. This doesn't happen if you leave the macro unset.
 329   .ifdef CHECK_RCPT_LOCAL_ACL_FILE
 330   .include CHECK_RCPT_LOCAL_ACL_FILE
 331   .endif
 332
 333
 334   #############################################################################
 335   # This check is commented out because it is recognized that not every
 336   # sysadmin will want to do it. If you enable it, the check performs
 337   # Client SMTP Authorization (csa) checks on the sending host. These checks
 338   # do DNS lookups for SRV records. The CSA proposal is currently (May 2005)
 339   # an Internet draft. You can, of course, add additional conditions to this
 340   # ACL statement to restrict the CSA checks to certain hosts only.
 341   #
 342   # require verify = csa
 343   #############################################################################
 344
 345
 346   # Accept if the address is in a domain for which we are an incoming relay,
 347   # but again, only if the recipient can be verified.
 348
 349   accept
 350     domains = +relay_to_domains
 351     endpass
 352     verify = recipient
 353
 354
 355   # At this point, the address has passed all the checks that have been
 356   # configured, so we accept it unconditionally.
 357
 358   accept