Spam Blocking in BSD with spamd: Part Two

spamdIn part one of this series, I discussed some of the advantages of spamd and how it works. In this article, I will cover spamd configuration.

spamd Configuration

Configuring the spamd daemon is pretty straightforward. First, you have to edit your rule set in /etc/pf.conf to include the following:

table persist
table persist
 pass on $ext_if inet proto tcp from <spamd> to \
( $ext_if, $localnet ) smtp rdr-to 127.0.0.1 port 8025
pass on $ext_if inet proto tcp from \

!<spamd-white> to ( $ext_if, $localnet ) port smtp rdr-to 127.0.0.1 port 8025

These rules set up two tables, (a table of known spammers) and (a list of whitelisted hosts which we assume are not spammers). SMTP traffic from the addresses in the first table () plus the ones not in the second table () is redirected to a daemon listening at port 8025 of the machine. The application which uses these tables, of course, is spamd, which is designed to waste spammers’ time and keep their traffic off our network.


You also need to edit your spamd.conf file (under FreeBSD. it should be located at /usr/local/etc/spamd/spamd.conf). First, you need to define which lists you will use:

all:\
:my_blacklist:my_whitelist:

This is where you add all the blacklists you want to use, separated by colons (:). If you want to use whitelists to subtract addresses from your blacklist, you add the name of the whitelist immediately after the name of each blacklist.

Next, you need to define your blacklist:

my_blacklist:\
:black:\
:msg=”SPAM. Your address %A has sent pam with the last 24 hours”:\
:method=http:\
:file=www.openbsd.org/spamd/traplist.gz

After the name, the first data field specifies the list type (black). The msg field contains the message to display to blacklisted senders during the SMTP dialogue. The method field specifies how spamd-setup fetches the list data. In this example, the type is http, but there are other options: you can fetch the list data via ftp, from a file in a mounted file system or via exec of an exernal program. The file filed specifies the name of the file spamd expects to receive.


You also need to define a whitelist:

my_whitelist:\
:white:\
:method=file:\
:file=/etc/mail/whitelist.txt

The whitelist in this example is similar to the blacklist, only the message parameter is omitted since it is not needed, and the source is a file on the local system.

You should be aware that enabling the suggested blacklists in the default spamd.conf could lead to blacklisting of large blocks of the internet, including several countries such as South Korea. Using other lists than the default ones is possible, and its within your discretion to use other ones or to make your own copy of the default blacklist and edit it as needed.

Next, put the lines for spamd and the startup parameters you want in /etc/rc.conf or /etc/rc.conf.local. In FreeBSD, spamd_grey has to be set to YES to enable greylisting (on OpenBSD 4.1 and later, spamd runs in greylisting mode by default and you need to set spamd_black to YES to run spamd in pure blacklisting mode. There are several parameters that can be used; see the spamd man page for a complete list of these options.

You can then view the table contents using pfctl or other applications. If you want to change or delete entries, you should use the spamdb utility, not pfctl. Also, note that if the redirection (rdr) rules you use do not include a “pass” part, you need to set up pass rules to let through traffic to your redirection, and also set up rules to let legitimate e-mail through.

External Links:

spamd man page at openbsd.org

The Apache SpamAssassin Project – download SpamAssassin here; you can also find SpamAssassin’s documentation.

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