man grossd.conf (5): Greylisting of Suspicious Sources daemon configuration file

SYNOPSIS

/etc/grossd.conf

DESCRIPTION

grossd(8) reads configuration data from /etc/grossd.conf (or the file specified with -f on the command line). An example configuration file is installed by default. You have to set some configuration options in order to get grossd(8) running in your environment. The format is as follows:

name = value [ ; param ] ...

Not all options accept parameters - refer to individual descriptions. The comment separator is `#', everything after it is ignored by the config file parser.

Network configuration options

host: is the address the server should listen for queries. Default is `localhost'.
port: is the port the server should listen for queries. Default is 5525.
sync_listen: is the address to listen for communication with the peer. It defaults to the host setting.
sync_peer: is the address of the peer used when running in clustered mode.
sync_port: is the tcp port number to listen to and connect to in communication with the peer. Default is 5524.
status_host: is the address grossd(8) listens for status queries. Default is `localhost'.
status_port: is the port number grossd(8) listens for status queries. Default is 5522.
protocol: activates the server protocols grossd(8) will support. Valid settings are `sjsms', `postfix' and `milter'.
milter_listen: is the socket address for the Milter service. The format is `proto:port@host'. Refer to Milter documentation for the specifics.

Core server options

You can probably leave the default values for these settings. If your daily mail flow exceeds millions of messages per day you may want to tweak query_timelimit and/or pool_maxthreads. If you run grossd(8) in a server with limited memory you may want to adjust filter_bits.

filter_bits: is the size of the Bloom filter. The size will be 2^filter_bits. Lowering this value will increase the probability of false matches in each individual filter. Default is 24.
number_buffers: is the number of Bloom filters used in the ring queue. Raising this value will cause an entry to stay in the server's memory longer. Default is 8.
rotate_interval: is the number of seconds between Bloom filter rotations. Let N := number_buffers and I := rotate_interval. An entry will stay in the server's memory for N - 0.5 * I seconds on average. Defaults to 3600 seconds (one hour).
update: is the way server updates the database. Valid options are `grey' and `always'. If set to `grey', which is the default, grossd(8) will update the database only if the response is `STATUS_GREY'. Setting it to `always' may reduce the impact on DNS servers.
grey_mask: is the mask for grossd(8) to use when matching the `smtp-client-ip' against the database. Default is 24, which makes grossd(8) to treat addresses like a.b.c.d as a.b.c.0. Setting grey_mask to 32 makes grossd(8) to require that consecutive attempts are made from the same `smtp-client-ip'.
statefile: is the full path of the file that the server uses to store the state information. Default is not to have a statefile. You may want to configure a statefile especially if you do not configure replication.
pidfile: is the full path of the file grossd(8) writes its pid into. You can set parameter `check', if you want to keep grossd(8) from starting should pidfile already exist.

Query constraints

grey_delay: is the time in seconds new triplets are kept on the greylist. Default is 180.
query_timelimit: is the query timeout in milliseconds. You may have to adjust this if you exceed millions of queries a day.
pool_maxthreads: is the maximum threadcount per pool. You may have to raise the limit from the default if you get more than 100 queries per second and/or have slow DNS servers. The rule of thumb is to decide how many queries you want grossd(8) to be able to handle per second, and multiply that with query_timelimit (in seconds, of course). It defaults to 100.

Configuring server responses

block_threshold: is the threshold after which grossd(8) sends a permanent error to the client. Every check that considers `smtp-client-ip' as suspicious returns a value (check weight). When sum of these values gets equivalent or greater than block_threshold grossd(8) sends a STATUS_BLOCK response. Default is 0 which disables this functionality.
block_reason: is the reason given when client is too suspicious, see block_threshold. Default is "Bad reputation".
grey_threshold: is analogous to block_threshold, except at the threshold grossd(8) sends a STATUS_GREY response. Default is 1. If set to 0 grossd(8) will greylist by default. This makes it possible to combine a traditional greylister and rbl checks.
grey_reason: is the reason given when client is suspicious enough to be greylisted, see grey_threshold. Default is "Please try again later.".

Logging options

log_method

is used to choose the logging method. Currently the only implemented method is `syslog', which is the default.

log_level

sets the logging verbosity. Possible values in the order of increasing verbosity are `error', `warning', `notice', `info' and `debug'. log_level defaults to `info'.

syslog_facility

is the facility syslog sends log messages with. It defaults to `mail'.

stat_type

is the name of the requested statistic. It is of multivalued type. The valid options are:

`full': log all possible statistics,
`none': no statistics logging,
`status': basic set of statistics,
`since_startup': basic set since the startup and
`delay': log processing delay statistics.

: Default is `none'. Setting both `none' and `full' is undefined.

stat_interval: is the number of seconds between status log entries. Default is 3600.

Configuring checks

check: is a multivalued option, that is, you can configure multiple checks by setting check option multiple times. Currently implemented checks are `dnsbl', `dnswl', `rhsbl' and `blocker'. Refer to sections describing the checks below. If you don't configure any checks grossd(8) will act as a traditional greylisting server.
dnsbl: is a DNS domain name of the dnsbl that `dnsbl' check will query. There are no defaults, but the default configuration file lists a few as an example. If you have any locally administered block lists then you should be aware that grossd(8) makes all queries as fully qualified. You may assign different weights for the dnsbls, default weight is 1. Refer to grey_threshold and block_threshold about the weights. dnsbl is a multivalued option.
dnswl: is analogous to dnsbl. Remember that dnswl is a definitive check, that is grossd(8) waits for the check to complete before deciding how to respond. This may cause unwanted latency, although you can adjust the maximum latency by query_timelimit option. dnswl is highly recommended if you use grossd(8) as a traditional greylister. This is a multivalued option.
rhsbl: is analogous to dnsbl, but the check is made with the right hand side of the sender address (the email domain) instead of the IP address. This is a multivalued option.
blocker_host: is the host name of the Sophos blocker server. This is used only if check = `blocker' is set.
blocker_port: is the TCP port of the Sophos blocker service. Default is 4466.
blocker_weight: is the weight of the blocker check. See description of grey_threshold and block_threshold regarding the weights.

Sun Java System Messaging Server specific options

You may configure the responses grossd(8) sends over to grosscheck library.

sjsms_response_grey: is the mapping result template grossd(8) uses for a STATUS_GREY result. Default is `$X4.4.3|$N%reason%', where `%reason%' is the template for the reason string.
sjsms_response_match: is the mapping result template grossd(8) uses for a STATUS_MATCH result. Default is `$Y'.
sjsms_response_trust: is the mapping result template grossd(8) uses for a STATUS_TRUST result. Default is `$Y'.
sjsms_response_block: is the mapping result template grossd(8) uses for a STATUS_BLOCK result. Default is `$N%reason%', where `%reason%' is the template for the reason string.

Postfix specific options

postfix_response_grey: is the response template grossd(8) uses for a STATUS_GREY result. Default is `action=defer_if_permit %reason%', where `%reason' is the template for the reason string.
postfix_response_block: is the response template grossd(8) uses for a STATUS_BLOCK result. Default is `action=reject %reason%', where `%reason' is the template for the reason string.

MTA CONFIGURATION

Sun Java System Messaging Server

You have to add a mapping entry to set SJSMS to query grossd(8). It's also a good idea to exclude postmaster and abuse addresses before querying grossd(8).

Here is an example:

  ORIG_MAIL_ACCESS

  ! allow all DSNs and MDNs
    TCP|*|*|*|*|*|*|tcp_local||*|*  $Y$E
  ! allow all incoming mail to postmaster and abuse
    TCP|*|*|*|*|*|*|tcp_local|*|*|postmaster@*  $Y$E
    TCP|*|*|*|*|*|*|tcp_local|*|*|abuse@*  $Y$E
  ! use gross to check all triplets (client_ip,sender,recipient)
    TCP|*|*|*|*|SMTP/*|*|tcp_local|*|*|*  $[/usr/lib/x86_64-linux-gnu/grosscheck.so,grosscheck,10.10.13.1,10.10.13.2,5525,$2,$=$8$_,$=$6$_,$=$4$_]

Mapping call parameters are as follows:

1. full path of the grosscheck.so
2. function name to call (always grosscheck)
3. first server's IP address,
4. second server's IP address,
5. UDP port for server connections,
6. SMTP client's IP address,
7. envelope sender's email address,
8. envelope recipient's email address,
9. HELO/EHLO string.

Postfix

Grossd implements native Postfix policy delegation protocol. Just specify grossd server address at the `smtpd_recipient_restrictions' in the main configuration file

main.cf :

  /etc/postfix/main.cf:
      smtpd_recipient_restrictions =
          ...
          reject_unauth_destination
          check_policy_service inet:host:port
          ...

Refer to Postfix documentation at <http://www.postfix.org> for specifics.

Exim

Exim can be configured to query grossd(8) via Postfix policy delegation protocol.

Main section:

  GROSS_QUERY = sender=$sender_address\\n\\
    recipient=$local_part@$domain\\n\\
    client_address=$sender_host_address\\n\\
    grossd_mode=single\\n\\n

Acl section:

  # gross
  warn
    set acl_c0 = ${readsocket{inet:127.0.0.1:5525}{GROSS_QUERY}}

  defer
    message = Please try again later.
    condition = ${if match {$acl_c0}{action=defer_if_permit}}

  deny
    message = ${if match {$acl_c0}{action=reject (.*)}{$1}\\
      {Rejected by Gross.}}
    condition = ${if match {$acl_c0}{action=reject}}

Sendmail

Sendmail can query grossd via milter protocol. Insert this in sendmail.mc and configure milter_listen accordingly:

INPUT_MAIL_FILTER(`Gross', `S=inet:5523@localhost, T=R:20s')

You can check if your version of Sendmail has Milter support compiled in by issuing the following command:

sendmail -bt -d0.1

AUTHORS

Eino Tuominen and Antti Siira