|SPAMD(8)||System Manager's Manual||SPAMD(8)|
spamdis a fake mail daemon which rejects false mail. It is designed to be very efficient so that it does not slow down the receiving machine.
spamd considers sending hosts to be of
blacklisted hosts are diverted to
spamd and tarpitted i.e. they are
communicated with very slowly to consume the sender's resources. Mail is
rejected with either a 450 or 550 error message. A blacklisted host will not
be allowed to talk to a real mail server.
whitelisted hosts do not talk to
spamd. Their connections are instead sent to a real
mail server, such as smtpd(8).
greylisted hosts are diverted to
spamd has not yet
decided if they are likely spammers. They are given a temporary failure
spamd when they try to deliver mail.
spamd is run in default mode, it will
greylist connections from new hosts. Depending on its configuration, it may
choose to blacklist the host or, if the checks described below are met,
eventually whitelist it. When
spamd is run in
blacklist-only mode, using the
-b flag, it will
consult a pre-defined set of blacklist addresses to decide whether to tarpit
the host or not.
When a sending host talks to
reply will be stuttered. That is, the response will be
sent back a character at a time, slowly. For blacklisted hosts, the entire
dialogue is stuttered. For greylisted hosts, the default is to stutter for
the first 10 seconds of dialogue only.
The options are as follows:
spamddoes not fork(2) into the background.
spamdis to bind(2). By default
spamdlistens on the localhost address 127.0.0.1.
spamdshould listen for diverted SMTP connections on. The default port is found by looking for the named service “spamd” using getservbyname(3).
spamdlogs connections, disconnections and blacklist matches to syslogd(8) at
LOG_INFOlevel. With verbose logging enabled, message detail including subject and recipient information is logged at
LOG_INFO, along with the message body and SMTP dialogue being logged at
When run in default mode, connections receive the pleasantly innocuous temporary failure of:
451 Temporary failure, please try again later.
This happens in the SMTP dialogue immediately after the DATA
command is received from the client.
spamd will use
the db file in /var/db/spamd to track these
spamd by connecting IP address,
HELO/EHLO, envelope-from, and envelope-to, or tuple for
short. Hosts which connect but do not attempt to deliver mail will not
generate a tuple and always be ignored.
A previously unseen tuple is added to the
/var/db/spamd database, recording the time an
initial connection attempt was seen. After passtime
spamd sees a retried attempt to deliver
mail for the same tuple,
spamd will whitelist the
connecting address by adding it as a whitelist entry to
spamd regularly scans the
/var/db/spamd database and configures all whitelist
addresses as the pf(4) <spamd-white>
table, allowing connections to pass to the real MTA. Any addresses not found
in <spamd-white> are diverted to
An example pf.conf(5) fragment
is given below. In the example, the file
/etc/mail/nospamd contains addresses of hosts who
should be passed directly to the SMTP agent (thus bypassing
table <spamd-white> persist table <nospamd> persist file "/etc/mail/nospamd" pass in on egress proto tcp to any port smtp \ divert-to 127.0.0.1 port spamd pass in on egress proto tcp from <nospamd> to any port smtp pass in log on egress proto tcp from <spamd-white> to any port smtp pass out log on egress proto tcp to any port smtp
spamd removes tuple entries from the
/var/db/spamd database if delivery has not been
retried within greyexp hours from the initial time a
connection is seen. The default is 4 hours as this is the most common
setting after which MTAs will give up attempting to retry delivery of a
spamd removes whitelist entries from the
/var/db/spamd database if no mail delivery activity
has been seen from the whitelisted address by
whiteexp hours from the initial time an address is
whitelisted. The default is 36 days to allow for the delivery of monthly
mailing list digests without greylist delays every time.
spamd-setup(8) should be
run periodically by cron(8) to update the
blacklists configured in
crontab(1) to uncomment the entry in
root's crontab. When run in blacklist-only mode, the
-b flag should be specified.
spamlogd(8) should be used to update the whitelist entries in /var/db/spamd when connections are seen to pass to the real MTA on the smtp port.
spamd sends log messages to
facility daemon and, with increasing verbosity,
level err, warn, info, and debug. The following
syslog.conf(5) section can be used
to log connection details to a dedicated file:
!spamd daemon.info /var/log/spamd
A typical entry shows the time of the connection and the IP
address of the connecting host. When a host connects, the total number of
active connections and the number of connections from blacklisted hosts is
shown (connected (xx/xx)). When a host disconnects, the amount of time spent
spamd is shown.
spamdin default mode, it may be useful to define spamtrap destination addresses to catch spammers as they send mail from greylisted hosts. Such spamtrap addresses affect only greylisted connections to
spamdand are used to temporarily blacklist a host that is obviously sending spam. Unused email addresses or email addresses on spammers' lists are very useful for this. When a host that is currently greylisted attempts to send mail to a spamtrap address, it is blacklisted for 24 hours by adding the host to the
spamdblacklist <spamd-greytrap>. Spamtrap addresses are added to the /var/db/spamd database with the following spamdb(8) command:
# spamdb -T -a 'email@example.com'
See spamdb(8) for further details.
The file /etc/mail/spamd.alloweddomains can be used to specify a list of domainname suffixes, one per line, one of which must match each destination email address in the greylist. Any destination address which does not match one of the suffixes listed in spamd.alloweddomains will be trapped, exactly as if it were sent to a spamtrap address. Comment lines beginning with ‘#’ and empty lines are ignored.
For example, if spamd.alloweddomains contains:
The following destination addresses would not cause the sending host to be trapped:
firstname.lastname@example.org email@example.com firstname.lastname@example.org
However the following addresses would cause the sending host to be trapped:
A low priority MX IP address may be specified with the
-M option. When
such an address specified, no host may enter new greylist tuples when
connecting to this address; only existing entries may be updated. Any host
attempting to make new deliveries to the low priority MX for which a tuple
has not previously been seen will be trapped.
Note that it is important to ensure that a host running
spamd with the low priority MX address active must
see all the greylist changes for a higher priority MX host for the same
domains. This is best done by the host itself receiving the connections to
the higher priority MX on another IP address (which may be an IP alias).
This will ensure that hosts are not trapped erroneously if the higher
priority MX is unavailable. For example, on a host which is an existing MX
record for a domain of value 10, a second IP address with MX of value 99 (a
higher number, and therefore lower priority) would ensure that any RFC
conformant client would attempt delivery to the IP address with the MX value
of 10 first, and should not attempt to deliver to the address with MX value
spamd. Any other addresses are passed to the real MTA.
table <spamd> persist pass in on egress inet proto tcp from <spamd> to any port smtp \ divert-to 127.0.0.1 port spamd
Addresses can be loaded into the table, like:
# pfctl -q -t spamd -T replace -f /usr/local/share/spammers
spamd-setup(8) can also be
used to load addresses into the <spamd> table. It has the added
benefit of being able to remove addresses from blacklists, and will connect
spamd over a localhost socket, giving
spamd information about each source of blacklist
addresses, as well as custom rejection messages for each blacklist source
that can be used to let any real person whose mail is deferred by
spamd know why their address has been listed from
sending mail. This is important as it allows legitimate mail senders to
pressure spam sources into behaving properly so that they may be removed
from the relevant blacklists.
spamdlistens for configuration connections on the port identified by the named service “spamd-cfg” (see services(5)). The configuration socket listens only on the INADDR_LOOPBACK address. Configuration of spamd is done by connecting to the configuration socket, and sending blacklist information, one blacklist per line. Each blacklist consists of a name, a message to reject mail with, and addresses in CIDR format, all separated by semicolons (;):
The rejection message must be inside double quotes. A \" will
produce a double quote in the output. \n will produce a newline. %A will
expand to the connecting IP address in dotted quad format. %% may be used to
produce a single % in the output. \\ will produce a single \.
spamd will reject mail by displaying all the
messages from all blacklists in which a connecting address is matched.
spamd-setup(8) is normally used to
configure this information.
spamdsupports realtime synchronisation of spamd databases between a number of spamd daemons running on multiple machines, using the
-yoptions. The databases are synchronised for greylisted and trapped entries; whitelisted entries and entries made manually using spamdb(8) are not updated.
The following example will accept incoming multicast and unicast synchronisation messages, and send outgoing multicast messages through the network interface em0:
# /usr/libexec/spamd -y em0 -Y em0
The second example will increase the multicast TTL to a value of 2, add the unicast targets foo.somewhere.org and bar.somewhere.org, and accept incoming unicast messages received on bge0 only.
# /usr/libexec/spamd -y bge0 -Y em0:2 \ -Y foo.somewhere.org -Y bar.somewhere.org
If the file /etc/mail/spamd.key exists,
spamd will calculate the message-digest fingerprint
(checksum) for the file and use it as a shared key to authenticate the
synchronisation messages. The file itself can contain any data. For example,
to create a secure random key:
# dd if=/dev/random of=/etc/mail/spamd.key bs=2048 count=1
The file needs to be copied to all hosts sending or receiving synchronisation messages.
spamdcommand first appeared in OpenBSD 3.3.
|July 24, 2019||OpenBSD-current|