Provided by: dcc-client_1.2.74-2_i386
dccproc - Distributed Checksum Clearinghouse Procmail Interface
dccproc [-VdAQCHER] [-h homedir] [-m map] [-w whiteclnt] [-T tmpdir]
[-a IP-address] [-f env_from] [-t targets]
[-x exitcode] [-c type,[log-thold,]rej-thold] [-g [not-]type]
[-S header] [-i infile] [-o outfile] [-l logdir]
[-B dnsbl-option] [-L ltype,facility.level]
Dccproc copies a complete SMTP message from standard input or a file to
standard output or another file. As it copies the message, it computes
the DCC checksums for the message, reports them to a DCC server, and adds
a header line to the message. Another program such as procmail(1) can
use the added header line to filter mail. Dccproc does not support any
thresholds of its own, because equivalent effects can be achieved with
regular expressions and you can apply dccproc several times using
different DCC servers and then score mail based what all of the DCC
Error messages are sent to stderr as well as the system log. Connect
stderr and stdout to the same file to see errors in context, but direct
stderr to /dev/null to keep DCC error messages out of the mail. The -i
option can also be used to separate the error messages.
Dccproc sends reports of checksums related to mail received by DCC
clients and queries about the total number of reports of particular
checksums. A DCC server receives no mail, address, headers, or other
information, but only cryptographically secure checksums of such
information. A DCC server cannot determine the text or other information
that corresponds to the checksums it receives. It only acts as a
clearinghouse of counts of checksums computed by clients.
For the sake of privacy for even the checksums of private mail, the
checksums of senders of purely internal mail or other mail that is known
to not be unsolicited bulk can be listed in a whitelist to not be
reported to the DCC server.
When sendmail(8) is used, dccm(8) is a better DCC interface. Dccifd(8)
is more efficient than dccproc because it is a daemon, but that has costs
in complexity. See dccsight(8) for a way to use previously computed
The following options are available:
-V displays the version of the DCC procmail(1) interface.
-d enables debugging output from the DCC client library. Additional -d
options increase the number of messages. One causes error messages
to be sent to STDERR as well as the system log.
-A adds to existing X-DCC headers (if any) of the brand of the current
server instead of replacing existing headers.
-Q only queries the DCC server about the checksums of messages instead
of reporting and then querying. This is useful when dccproc is used
to filter mail that has already been reported to a DCC server by
another DCC client such as dccm(8). This can also be useful when
applying a private white or black list to mail that has already been
reported to a DCC server. No single mail message should be reported
to a DCC server more than once per recipient, such as would happen
if dccproc is not given -Q when processing a stream of mail that has
already been seen by a DCC client. Additional reports of a message
increase its apparent "bulkness."
-C outputs only the X-DCC header and the checksums for the message.
-H outputs only the X-DCC header.
-E adds lines to the start of the log file turned on with -l and -c
describing what might have been the envelope of the message. All of
the information for the envelope lines comes from arguments to
dccproc including -a and -R. No lines are generated for which no
information is available, such as the envelope recipient.
-R says the first Received line has a standard "name (name [IP
address])..." format and that the address is the IP address of the
SMTP client that would otherwise be provided with -a. If the local
SMTP server adds a Received line with some other format or does not
add a Received line, the -a option should be used.
overrides the default DCC home directory, which is often /var/dcc.
specifies a name or path of the memory mapped parameter file instead
of the default map in the DCC home directory. It should be created
with the new map operation of the cdcc(8) command.
specifies an optional file containing SMTP client IP addresses and
SMTP headers of mail that do not need X-DCC headers and whose
checksums should not be reported to the DCC server. It can also
contain checksums of spam. If the pathname is not absolute, it is
relative to the DCC home directory. Thus, individual users with
private whitelists usually specify them with absolute paths. Common
whitelists shared by users must be in the DCC home directory or one
of its subdirectories and owned by the set-UID user of dccproc. It
is useful to include a common or system-wide whitelist in private
The format of the dccproc whiteclnt file is the same as the
whitelist file required by dbclean(8) and dccm(8). Unlike dccm, the
dccproc whitelist is optional. Unless -w is used, dccproc uses only
the whitelist in the DCC server, which is rarely sufficient.
Because the contents of the whiteclnt file are used frequently, a
companion file is automatically created and maintained. It has the
same pathname but with an added suffix of .dccw. It contains a
memory mapped hash table of the main file.
A local whitelist entry ("OK) or two or more semi-whitelistings
("OK2") for one of the message’s checksums prevents all of the
message’s checksums from being reported to the DCC server and the
addition of a X-DCC header line by dccproc. Because it is run by or
on behalf of a single user, dccproc ignores env_To entries in the
whiteclnt file. Users who don’t want to use dccproc shouldn’t.
changes the default directory for temporary files from the default.
The default is the directory specified with -l or the system default
if there -l is not used. The system default is often /tmp.
specifies the IP address (not the host name) of the immediately
previous SMTP client. It is often not available. See also -R.
specifies the RFC 821 envelope "Mail From" value with which the
message arrived. It is often not available. If -f is not present,
the contents of the first Return-Path: or UNIX style From_ header is
used. The env_from string is often but need not be bracketed with
specifies the number of addressees of the message if other than 1.
The string many instead of a number asserts that there were too many
addressees and that the message is unsolicited bulk email.
specifies the code or status with which dccproc exits if the -c
thresholds are reached or the -w whiteclnt file blacklists the
message, unless the message is whitelisted.
The default value is EX_NOUSER. EX_NOUSER is 67 on many systems.
Use 0 to always exit successfully.
sets logging and "spam" thresholds for checksum type. Each logged
message placed in a separate file in the directory specified with
-l. The checksum types are IP, env_From, From, Message-ID,
Received, Body, Fuz1, and Fuz2. The string ALL sets thresholds for
all types, but is unlikely to be useful except for setting logging
thresholds. The string CMN specifies the commonly used checksums
Body, Fuz1, and Fuz2. Rej-thold and log-thold must be numbers, the
string NEVER, or the string MANY indicating millions of targets.
Counts from the DCC server as large as the threshold for any single
type are taken as sufficient evidence that the message should be
logged or rejected.
Log-thold is the threshold at which messages are logged. It can be
handy to log messages at a lower threshold to find solicited bulk
mail sources such as mailing lists. Messages that reach at least
one of their rejection thresholds or that have complicated
combinations of white- and blacklisting are logged regardless of
Rej-thold is the threshold at which messages are considered "bulk,"
and so should cause the X-DCC header line to contain the string
"bulk" and dccproc to exit with the value set by -x.
The checksums of locally white-listed messages are not checked with
the DCC server and so only the number of targets of the current
instance of a white-listed message are compared against the
The default is -c ALL,NEVER, so that nothing is discarded or logged.
A common choice is -c CMN,25,50 to reject or discard mail with
common bodies except as overridden by the whitelist of the DCC
server and -g and -w.
indicates that white-listed, OK or OK2, counts from the DCC server
for a type of checksum are to be believed. They should be ignored
if prefixed with not-. Type is one of the same set of strings as
for -c. Only IP, env_From, and From are likely choices. By default
all three are honored, and hence the need for not-.
adds to the list of substitute or locally chosen headers that are
checked with the -w whiteclnt file and sent to the DCC server. The
checksum of the last header of type hdr found in the message is
checked. As many as 6 different substitute headers can be
specified, but only the checksum of the first of the 6 will be sent
to the DCC server.
specifies an input file for the entire message instead of standard
input. If not absolute, the pathname is interpreted relative to the
directory in which dccproc was started.
specifies an output file for the entire message including headers
instead of standard output. If not absolute, the pathname is
interpreted relative to the directory in which dccproc was started.
specifies a directory for copies of messages whose checksum target
counts exceed -c thresholds. The format of each file is affected by
-E. If logdir is not an absolute path, it is relative to the
directory in which dccproc is started. If logdir starts with D?,
log files are put into subdirectories of the form logdir/JJJ where
JJJ is the current julian day. H?logdir puts logs files into
subdirectories of the form logdir/JJJ/HH where HH is the current
hour. M?logdir puts log files into subdirectories of the form
logdir/JJJ/HH/MM where MM is the current minute. See the FILES
section below concerning the contents of the files.
The directory is relative to the DCC home directory if it is not
enables DNS blacklist checks of the SMTP client IP address, SMTP
envelope Mail_From sender domain name, and of host names in URLs in
the message body. Body URL blacklisting has far too many false
positives to use on abuse mailboxes. It is less effective than
greylisting with dccm(8) or dccifd(8) but can be useful in
situations where greylisting cannot be used.
Dnsbl-option is either of the form set:option or of the form
domain[,IPaddr[,bltype]]. Domain is a DNS blacklist domain such as
example.com that will be searched. IPaddr is the IP address in the
DNS blacklist that indicates that the mail message is spam.
127.0.0.1 is assumed if IPaddr is absent. IPv6 addresses can be
specified with the usual colon (:) notation. Names can be used
instead of numeric addresses. The type of DNS blacklist is
specified by bltype as name, IPv4, or IPv6. Given an envelope
sender domain name or a domain name in a URL of spam.domain.org and
a blacklist of type name, spam.domain.org.example.com will be tried.
Blacklist types of IPv4 and IPv6 require that the domain name in a
URL be resolved into an IPv4 or IPv6 address. The address is then
written as a reversed string of decimal octets to check the DNS
blacklist, as in 18.104.22.168.example.com,
More than one blacklist can be specified. They are searched in
order. All searching is stopped at the first positive result.
Positive results are ignored after being logged unless an option
DNSBL-on line appears in the global or per-user whiteclnt file.
-B set:debug sends more messages about all DNS resolutions to the
-B set:msg-secs=S limits dccproc to S seconds total for checking all
DNS blacklists. The default is 20.
-B set:URL-secs=S limits dccproc to at most S seconds resolving and
checking any single URL. The default is 5. Some spam contains
dozens of URLs and that some "spamvertised" URLs contain host names
that need minutes to resolve. Busy mail systems cannot afford to
spend minutes checking each incoming mail message. In order to use
typical single-threaded DNS resolver libraries, dccm(8) and
dccifd(8) use fleets of helper processes.
-B set:no-envelope says that SMTP client IP addresses and sender
Mail_From domain names should not be checked in the following
blacklists. -B set:envelope restores the default for subsequently
-B set:no-body says that URLs in the message body should not be
checked in the in the following blacklists. -B set:body restores
the default for later blacklists.
-B set:no-MX says MX servers of sender Mail_From domain names and
host names in URLs should not be checked in the following
blacklists. -B set:MX restores the default.
specifies how messages should be logged. Ltype must be error or
info to indicate which of the two types of messages are being
controlled. Level must be a syslog(3) level among EMERG, ALERT,
CRIT, ERR, WARNING, NOTICE, INFO, and DEBUG. Facility must be among
AUTH, AUTHPRIV, CRON, DAEMON, FTP, KERN, LPR, MAIL, NEWS, USER,
UUCP, and LOCAL0 through LOCAL7. The default is equivalent to
-L info,MAIL.NOTICE -L error,MAIL.ERR
Something like this turns off the log messages:
-L notice,MAIL.debug -L error,MAIL.DEBUG
dccproc exits 0 on success and with the -x value if the -c thresholds are
reached or the -w whiteclnt file blacklists the message. If at all
possible, the input mail message is output to standard output or the -o
outfile despite errors. If possible, error messages are put into the
system log instead of being mixed with the output mail message. The exit
status is zero for errors so that the mail message will not be rejected.
/var/dcc DCC home directory in which other files are found.
map memory mapped file in the DCC home directory of information
concerning DCC servers.
whiteclnt contains the client whitelist in the format described in
is a memory mapped hash table corresponding to the whiteclnt
tmpdir contains temporary files created and deleted as dccproc
processes the message.
logdir is an optional directory specified with -l and containing
marked mail. Each file in the directory contains one message,
at least one of whose checksums reached one of its -c
thresholds. The entire body of the SMTP message including its
header is followed by the checksums for the message.
The following procmailrc(5) rule adds an X-DCC header to passing mail
| /usr/local/bin/dccproc -ERw whiteclnt
This procmailrc(5) recipe rejects mail with total counts of 10 or larger
for the commonly used checksums:
| /usr/local/bin/dccproc -ERw whiteclnt -ccmn,10
cdcc(8), dcc(8), dbclean(8), dccd(8), dblist(8), dccifd(8), dccm(8),
dccsight(8), mail(1), procmail(1).
Implementation of dccproc was started at Rhyolite Software in 2000. This
describes version 1.2.74.
dccproc uses -c where dccm(8) uses -t.