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.

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:

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.

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:

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