grossd - Greylisting of Suspicious Sources - the Server
grossd [-dCDhnrV] [-fconfig]
grossd is a greylisting server, and more. It's blazingly fast and
amazingly resource efficient. It can be configured to query DNSBL
databases, and enforce greylisting only for hosts that are found on those databases.
It can block hosts that match multiple databases. It can be replicated and run parallel
on two servers. It supports Sun Java System Messaging Server,
Postfix and Exim. Sendmail Milter implementation needs testing.
Theory of operation
Gross consists of grossd,
the greylisting daemon, and a client library for SJSMS.
The server also implements Postfix content filtering protocol.
Upon receiving a request from a client, grossd first validates it.
The request includes a triplet (`smtp-client-ip', `sender-address',
A hash is then calculated and matched against the Bloom filters. If a
match is found, and test result does not exceed block_threshold
value, grossd sends an OK (STATUS_TRUST) message.
If the triplet is not in the Bloom filters (has not been seen recently,) grossd then
runs configured checks against the client information.
Based on check results grossd returns the client
a result. Possible results are STATUS_TRUST, STATUS_BLOCK
and STATUS_GREY. The final response is query protocol specific.
The Bloom filters are updated according the
update configuration option. A Bloom filter is a
very efficient way to store data. It's a probabilistic data
structure, which means that there is a possibility of error when
querying the database. False positives are possible, but false
negatives are not. This means that there is a possibility
that grossd will falsely give an STATUS_TRUST response when a
connection should be greylisted. By sizing the bloom
filters, you can control the error possibility to meet your
needs. The right bloom filter size depends on the number
of entries in the database, that is, the retention time
versus the number of handled connections.
Create the statefile and exit. The statefile configuration option
must be specified in the configuration file.
Make debugging output more verbose. It can be set twice
for maximum verbosity.
Run grossd on foreground without daemonizing the process.
grossd will output to terminal instead of using syslog.
Specifies the name of the configuration file. The default is
Output short usage information and exit.
Bail out if the pidfile already exists. Create pidfile after the check.
Create the pidfile. Overwrite if it already exists.
Output version information and exit.
Run grossd under some unprivileged user id. If started as root
grossd will setuid() itself to nobody's user id. There are no
known security flaws but you must not expose grossd
to the Internet. It could be used for a DoS against a domain's
DNS servers by an attacker as there is no authentication in grossd.
grossd daemon exits 0 if success, and >0 if an error occurs.
Regarding the configuration both the daemon and MTA's, refer to