dccproc(8)              FreeBSD System Manager's Manual             dccproc(8)


     dccproc -- Distributed Checksum Clearinghouse Procmail Interface


     dccproc [-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]


     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 -o
     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 in-
     formation, 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

     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 program's version.  Two or more -V options show the op-
          tions 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 /var/dcc/whiteclnt
          file for your MX mail servers that use DCC than to use -Q with

          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 de-
          scribing what might have been the envelope of the message.  The in-
          formation 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 re-

     -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 [ad-
          dress])..."  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 ad-
          dresses marked MX or MXDCC in the -w whiteclnt file are skipped.

     -h homedir
          overrides the default DCC home directory, /var/dcc.

     -m map
          specifies a name or path of the memory mapped parameter file instead
          of the default /var/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

          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 is ig-
          nored.  -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-

          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

          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 re-
          jected.  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

          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 ab-

     -B dnsbl-option
          enables DNS white- and blacklist checks of the SMTP client IP ad-
          dress, 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 effective
          than greylisting with dccm(8) or dccifd(8) but can be useful in sit-
          uations where greylisting cannot be used.  It can be combined with

          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.  "" 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 ad-
          dress be resolved into an IPv4 or IPv6 address.  The resolved ad-
          dress from the mail message is then written as a reversed string of
          decimal octets to check the DNS blacklist, as in

          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
          with an informative status message:

            '-Bset:rej-msg=5.7.1 550 %ID %BTYPE \

          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-

          -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,
          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.


     /var/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
                is a memory mapped hash table corresponding to the whiteclnt
     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.


     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


     cdcc(8), dcc(8), dbclean(8), dccd(8), dblist(8), dccifd(8), dccm(8),
     dccsight(8), mail(1), procmail(1).


     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 RHYOLITE_VERSION.


     dccproc uses -c where dccm(8) uses -t.

                                March 22, 2024

Man(1) output converted with man2html modified for DCC $Date 2001/04/29 03:22:18 $