dccproc(8) Distributed Checksum Clearinghouse dccproc(8)NAMEdccproc — Distributed Checksum Clearinghouse Procmail Interface
SYNOPSISdccproc [-VdAQCHEPR] [-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]
DESCRIPTION
Dccproc is a low performance DCC client for checking single mail messages
for mail filters such as procmail(1)
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 or the exit dccproc exit status.
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 informa‐
tion. A DCC server cannot determine the text or other information that
corresponds to the checksums it receives. It only acts as a clearing‐
house of counts of checksums computed by clients.
The checksums of private mail, the internal mail,and other mail that is
known to not be unsolicited bulk can be listed in a whitelist specified
with
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
checksums.
OPTIONS
The following options are available:
-V displays the program's version. Two or more -V options show the
options with which it was built.
-d enables debugging output from the DCC client software. Additional
-d options increase the number of messages. One causes error mes‐
sages to be sent to STDERR as well as the system log.
-A adds to existing X-DCC headers in the message instead of replacing
existing headers of the brand of the current server.
-P The SpamAsassin DCC.pm plugin should watch for "bulk" in X-DCC SMTP
header fields, but historically has looked for counts of "many".
However, there are situations when dccproc knows that a mail message
is extremely bulky and probably spam. For example, mail from a
sender that is blacklisted in whiteclnt gets an X-DCC header that
includes bulk. To acommodate that bug in SpamAssassin, by default
whenever dccproc generates an X-DCC header containing "bulk", it
also forces the Body count to "many". -P turns off that kludge and
the Body contains the count from the DCC server.
-Q only queries the DCC server about the checksums of messages instead
of reporting. This is useful when dccproc is used to filter mail
that has already been reported to a DCC server by another DCC
client. No single mail message should be reported to a DCC server
more than once per recipient, because each report will increase the
apparent "bulkness" of the message.
It is better to use MXDCC lines in the global
/usr/local/dcc/whiteclnt file for your MX mail servers that use DCC
than to use -Q with dccproc.
Do not use -Q except on mail that you know has been reported to a
DCC server. DCC depends on reports of all except known private mail
and works only because almost no DCC installations use -Q.
-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. The
information for the inferred envelope comes from arguments including
-a and headers in the message when -R is used. No lines are gener‐
ated for which no information is available, such as the envelope
recipient.
-P The SpamAsassin DCC.pm plugin should watch for "bulk" in X-DCC SMTP
header fields, but historically has looked for counts of "many".
However, there are situations when dccproc knows that a mail message
is extremely bulky and probably spam. For example, mail from a
sender that is blacklisted in whiteclnt gets an X-DCC header that
includes bulk. To acommodate that bug in SpamAssassin, by default
whenever dccproc generates an X-DCC header containing "bulk", it
also forces the Body count to "many". -P turns off that kludge and
the Body contains the count from the DCC server.
-R says the first Received lines have the standard
"helo (name [address])..." format and the address is that of the
SMTP client that would otherwise be provided with -a. The -a option
should be used if the local SMTP server adds a Received line with
some other format or does not add a Received line. Received headers
specifying IP addresses marked MX or MXDCC in the -w whiteclnt file
are skipped.
-h homedir
overrides the default DCC home directory, /usr/local/dcc.
-m map
specifies a name or path of the memory mapped parameter file instead
of the default /usr/local/dcc/map. It should be created with the
new map operation of the cdcc(8) command.
-w whiteclnt
specifies an optional file containing SMTP client IP addresses and
SMTP headers of mail that do not need X-DCC headers and whose check‐
sums 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
lists.
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 mem‐
ory mapped hash table of the main file.
Option lines can be used to modify many aspects of dccproc filter‐
ing, as described in the main dcc(8) man page. For example, an
option spam-trap-discards line turns off DCC filtering and reports
the message as spam.
-T tmpdir
changes the default directory for temporary files from the system
default. The system default is often /tmp.
-a IP-address
specifies the IP address (not the host name) of the immediately pre‐
vious SMTP client. It is often not available. -a 0.0.0.0 is
ignored. -a. The -a option should be used instead of -R if the
local SMTP server adds a Received line with some other format or
does not add a Received line.
-f env_from
specifies the RFC 821 envelope "Mail From" value with which the mes‐
sage 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
"<>".
-t targets
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.
-x exitcode
specifies the code or status with which dccproc exits if the -c
thresholds are reached or the -w whiteclnt file blacklists the mes‐
sage.
The default value is EX_NOUSER. EX_NOUSER is 67 on many systems.
Use 0 to always exit successfully.
-c type,[log-thold,]rej-thold
sets logging and "spam" thresholds for checksum type. The checksum
types are IP, env_From, From, Message-ID, substitute, Received,
Body, Fuz1, Fuz2, rep-total, and rep. The first six, IP through
substitute, have no effect except when a local DCC server configured
with -K is used. The substitute thresholds apply to the first sub‐
stitute heading encountered in the mail message. The string ALL
sets thresholds for all types, but is unlikely to be useful except
for setting logging thresholds. The string CMN specifies the com‐
monly 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. If no logging threshold is set,
only rejected mail and messages with complicated combinations of
white and blacklisting are logged. Messages that reach at least one
of their rejection thresholds are logged regardless of logging
thresholds.
Rej-thold is the threshold at which messages are considered "bulk,"
and so should be rejected or discarded if not whitelisted.
DCC Reputation thresholds in the commercial version of DCC are con‐
trolled by thresholds on checksum types rep and rep-total. The DCC
Reputations of IP addresses that the DCC database says have sent
more than rep-total,log-thold are computed and messages from those
addresses are logged. Messages from IP addresses with DCC Reputa‐
tions of at least the rep,rej-thold rejection threshold can be
rejected. The DCC Reputation of an IP address is the percentage of
its messages known to have been sent to at least 10 recipients. The
defaults are equivalent to rep,never and rep-total,never,20.
Bulk DCC Reputations do not reject mail unless enabled by an
option DCC-rep-on line a whiteclnt file.
The checksums of locally whitelisted messages are not checked with
the DCC server and so only the number of targets of the current copy
of a whitelisted message are compared against the thresholds.
The default is ALL,NEVER, so that nothing is discarded, rejected, or
logged. A common choice is CMN,25,50 to reject or discard mail with
common bodies except as overridden by the whitelist of the DCC
server, the sendmail ${dcc_isspam} and ${dcc_notspam} macros, and
-g, and -w.
-g [not-]type
indicates that whitelisted, 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-.
-S hdr
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. Hdr can be HELO to specify the SMTP envelope HELO value.
Hdr can also be mail_host to specify the host name from the
Mail_from value in the SMTP envelope. As many as 8 different sub‐
stitute headers can be specified, but only the checksum of the first
will be sent to the DCC server.
-i infile
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.
-o outfile
specifies an output file for the entire message including headers
instead of standard output. If not absolute, the pathname is inter‐
preted relative to the directory in which dccproc was started.
-l logdir
specifies a directory for copies of messages whose checksum target
counts exceed -c thresholds. The format of each file is affected by
-E.
See the FILES section below concerning the contents of the files.
See also the option log-subdirectory-{day,hour,minute} lines in
whiteclnt files described in dcc(8).
The directory is relative to the DCC home directory if it is not
absolute
-B dnsbl-option
enables DNS white- and 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 too
many false positives to use on abuse mailboxes. It is less effec‐
tive than greylisting with dccm(8) or dccifd(8) but can be useful in
situations where greylisting cannot be used. It can be combined
with greylisting.
Dnsbl-option is either one of the -B set:option forms or
-B domain[any[,bltype]]
-B domain[,IPaddr[/xx[&IPmask][,bltype]]]
-B domain[,IPaddrLO[-IPaddrHI[&IPmask][,bltype]]]
Domain is a DNS blacklist domain such as example.com that will be
searched. The strings any, IPaddr, IPaddr/xx, or IPaddrLO-IPaddrHI,
specifies which IP addresses found in the DNS blacklist after apply‐
ing the optional IP address mask IPmask say that mail messages
should be rejected or accepted with -B set:white. "127.0.0.2" is
assumed if no address(es) are specified. IPv6 addresses can be
specified with the usual colon (:) notation. Host names can be used
instead of numeric addresses. The type of DNS blacklist is speci‐
fied by bltype as name, all-names, 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 looked
up. The names spam.domain.org.example.com, domain.org.example.com,
and org.example.com will be looked up in blacklists of type
all-names. Use name with DNS blacklists that use wildcards for
speed but all-names for other DNS name blacklists. Blacklist types
of IPv4 and IPv6 require that the domain name in a URL sender
address be resolved into an IPv4 or IPv6 address. The resolved
address from the mail message is then written as a reversed string
of decimal octets to check the DNS blacklist, as in
2.0.0.127.example.com.
A domain of "." and type of name can be used to blacklist domain
names with specified addresses. This can be useful to detect URLs
with domain names listed in a Response Policy Zone (RPZ). For exam‐
ple, the following can be used to reject mail containing URLs listed
by a response policy zone that maps evil domain names to 224.0.0.0
with an informative status message:
'-Bset:rej-msg=5.7.1 550 %ID %BTYPE \
http://example.com/query/dbl?domain=%BTGT'
-B.,224.0.0.0,name
More than one blacklist can be specified and blacklists can be
grouped with -B set:group=X. All searching within a group of black‐
lists is stopped at the first positive result.
Unlike dccm(8) and dccifd(8), no option DNSBL-on line is required in
the whiteclnt file. A -B argument is sufficient to show that DNSBL
filtering is wanted by the dccproc user.
-B set:no-client
implies that SMTP client IP addresses and reverse DNS domain
names should not be checked in the following blacklists.
-B set:client restores the default for the following black‐
lists.
-B set:no-mail_host
implies that SMTP envelope Mail_From sender domain names should
not be checked in the following blacklists. -B set:mail_host
restores the default.
-B set:no-URL
says that URLs in the message body should not be checked in the
in the following blacklists. -B set:URL restores the default.
-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.
-B set:no-NS
says DNS servers of sender Mail_From domain names and host
names in URLs should not be checked in the following black‐
lists. -B set:NS restores the default.
-B set:white
says the DNS list is a whitelist of names or IP addresses.
-B set:black restores the default. DNS whitelist usually also
need -B set:no-mail_host, -B set:no-URL, -B set:no-MX,
-B set:no-NS, and -B set:no-mail_host.
-B set:defaults
is equivalent to all of -B set:black -B set:client
-B set:mail_host -B set:URL -B set:MX and -B set:NS
-B set:group=X
adds following DNS blacklists specified with -B domain[...] to
group 1, 2, 3, or 4.
-B set:debug=X
sets the DNS blacklist logging level
-B set:msg-secs=S
limits dccproc to S seconds total for checking all DNS black‐
lists. The default is 25.
-B set:URL-secs=S
limits dccproc to at most S seconds resolving and checking any
single URL or IP address. The default is 11. Some spam con‐
tains dozens of URLs and some "spamvertised" URLs contain host
names that need minutes to resolve. Busy mail systems cannot
afford to spend minutes checking each incoming mail message.
-L ltype,facility.level
specifies how messages should be logged. Ltype must be error, info,
or off to indicate which of the two types of messages are being con‐
trolled or to turn off all syslog(3) messages from dccproc. 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
dccproc exits with 0 on success and with the -x value if the -c thresh‐
olds 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.
If dccproc is run more than 500 times in fewer than 5000 seconds, dccproc
tries to start Dccifd(8). The attempt is made at most once per hour.
Dccifd is significantly more efficient than dccproc. With luck, mecha‐
nisms such as SpamAssassin will notice when dccifd is running and switch
to dccifd.
FILES
/usr/local/dcc
DCC home directory.
map memory mapped file in the DCC home directory of information
concerning DCC servers.
whiteclnt contains the client whitelist in the format described in
dcc(8).
whiteclnt.dccw
is a memory mapped hash table corresponding to the whiteclnt
file.
tmpdir contains temporary files created and deleted as dccproc pro‐
cesses 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 thresh‐
olds. The entire body of the SMTP message including its
header is followed by the checksums for the message.
EXAMPLES
The following procmailrc(5) rule adds an X-DCC header to passing mail
:0 f
| /usr/local/bin/dccproc -ERw whiteclnt
This procmailrc(5) recipe rejects mail with total counts of 10 or larger
for the commonly used checksums:
:0 fW
| /usr/local/bin/dccproc -ERw whiteclnt -ccmn,10
:0 e
{
EXITCODE=67
:0
/dev/null
}
SEE ALSOcdcc(8), dcc(8), dbclean(8), dccd(8), dblist(8), dccifd(8), dccm(8),
dccsight(8), mail(1), procmail(1).
HISTORY
Distributed Checksum Clearinghouses are based on an idea of Paul Vixie.
Implementation of dccproc was started at Rhyolite Software in 2000. This
document describes version 1.3.158.
BUGSdccproc uses -c where dccm(8) uses -t.
April 03, 2015
