Provided by: opendkim_2.11.0~alpha-12_amd64 bug

NAME

       opendkim - DKIM signing and verifying filter for MTAs

SYNOPSIS

       opendkim  [-A]  [-b modes] [-c canon] [-d domain[,...]]  [-D] [-e name] [-f] [-F time] [-k
       keyfile] [-l] [-L min] [-n] [-o hdrlist]  [-p  socketspec]  [-P  pidfile]  [-Q]  [-r]  [-s
       selector]  [-S  signalg]  [-t  testfiles] [-T secs] [-u userid[:group]] [-v] [-V] [-W] [-x
       configfile] [-X]

DESCRIPTION

       opendkim implements the DKIM standard for signing and verifying e-mail messages on a  per-
       domain basis.

       opendkim  uses  the  milter  interface,  originally distributed as part of version 8.11 of
       sendmail(8), to provide DKIM signing  and/or  verifying  service  for  mail  transiting  a
       milter-aware MTA.

       Most,  if  not  all,  of  the  command  line  options listed below can also be set using a
       configuration file.  See the -x option for details.

DATA SETS

       Many of the command line and configuration file parameters will refer to  a  "dataset"  as
       their  values.  This refers to a string that either contains the list of desirable values,
       or to a file that contains them, or (if enabled at compile time) a database containing the
       data.

       Some  data  sets  require  that  the  value contain more than one entry.  How this is done
       depends on which data set type is used.

       Which type is used depends on the format of the specification string.  Note that  not  all
       of  these  are  necessarily  supported  for  all installations; most of them depend on the
       availability of a particular third-party library at compile time.

       In particular:

       a)     If the string begins with "file:", then the remainder of the string is presumed  to
              refer  to  a  flat file that contains elements of the data set, one per line.  If a
              line contains whitespace-separated values, then the line is presumed  to  define  a
              key  and  its  corresponding  value.   Blank  lines are ignored, and the hash ("#")
              character denotes the start of a comment.  If a value  contains  multiple  entries,
              the entries should be separated by colons.

       b)     If  the  string begins with "refile:", then the remainder of the string is presumed
              to specify a file that contains  a  set  of  patterns,  one  per  line,  and  their
              associated  values.   The  pattern  is  taken as the start of the line to the first
              whitespace, and the portion after that whitespace is taken as the value to be  used
              when  that pattern is matched.  Patterns are simple wildcard patterns, matching all
              text except that the asterisk ("*") character is considered a wildcard.  If a value
              contains multiple entries, the entries should be separated by colons.

       c)     If  the  string  begins  with  "db:" and the program was compiled with Sleepycat DB
              support, then the remainder of the string  is  presumed  to  identify  a  Sleepycat
              database  containing keys and corresponding values.  These may be used only to test
              for membership in the data set, or for storing keys and corresponding values.  If a
              value contains multiple entries, the entries should be separated by colons.

       d)     If  the  string begins with "dsn:" and the OpenDKIM library was compiled to support
              that database type, then  the  remainder  of  the  string  is  a  Data  Store  Name
              describing  the type, location parameters and access credentials for an ODBC or SQL
              database.  The DSN is of the form:

              backend://[user[:pwd]@][port+]host/dbase[/key=value[?...]]

              where backend is the name of a supported backend database mechanism (e.g. "mysql"),
              user  and  password  are optional login credentials for the database, port and host
              describe the destination of a TCP connection to connect to that database, dbase  is
              the  name  of  the database to be accessed, and the key=value pairs must specify at
              least "table", "keycol" and "datacol" values specifying the name of the table,  the
              name  of  the column to consider as the key, and the name(s) of the column(s) to be
              considered as the values (separated by commas).  For example (all in one line):

              mysql:://dbuser:dbpass@3306+dbhost/odkim/table=macros
                       ?keycol=host?datacol=v1,v2

              defines a MySQL database listening at  port  3306  on  host  "dbhost";  the  userid
              "dbuser"  and password "dbpass" should be used to access the database; the database
              name is "odkim", and the data are in columns "host" (the keys) and  "v1"  and  "v2"
              (the values) inside table "macros".  This example would thus return two values when
              a match is found.

              The key may also include a "filter" value which will be included in  all  generated
              SQL as an AND clause after the WHERE clause that declares the search criteria.  For
              example, given the above DSN specification with an additional "filter" value of "ID
              > 1000", the generated SQL for a query for "foo" would look like so:

              SELECT v1,v2 FROM macros WHERE host = 'foo' AND ID > 1000

              No  value  within  the  DSN may contain any of the six punctuation characters (":",
              "/", "@", "+", "?" and "=") used to delimit portions of the DSN.  To  include  such
              characters  within a value, encode them in quoted-printable style (e.g., "=20" will
              be translated into a single space character).  Encoding of spaces is also advised.

       e)     If the string begins with "ldap:", "ldaps:" or "ldapi:", it is  presumed  to  be  a
              space-separated  set  of one or more LDAP URLs that identify a set of servers to be
              queried.  The first one should be a full RFC4516 LDAP  URL  indicating  a  base  DN
              template  and  optional  scope, filter and attribute names to use in queries.  When
              constructing a DN template or filter, the special tokens "$d" and "$D" are replaced
              with  the  key  being  queried and the key broken into components, separated at "."
              characters, each component preceded by "dc=" and followed by "," (so  "example.com"
              would  become  "dc=example,dc=com").   If a data set requires multiple values to be
              returned, the appropriate attribute names should be given in the correct  order  to
              satisfy such requests.

       f)     If the string begins with "lua:", it is presumed to refer to a file that contains a
              Lua script to be executed whenever a query is performed.  The key for the query  is
              placed  in  a  global  variable  called  "query",  which the called script can then
              access.  The script may return any number of values as required  for  the  type  of
              query being performed.

       g)     If  the  string  begins with "memcache:", it is presumed to refer to a memory cache
              database provided by memcached.  The remainder of the string is  a  comma-separated
              list  of  hosts to which query attempts should be made, each optionally followed by
              ":" and a port number; that list must be followed by a slash ("/") character and  a
              string that will be used to prefix queries send to the cache.  For example:

              memcache:localhost,otherhost/keyname

              This  would  use  either  "localhost"  or  "otherhost"  to conduct queries, and all
              strings sent to the dataset will be prefixed with "keyname:".

       h)     If the string contains none of these prefixes but ends with ".db", it  is  presumed
              to be a Sleepycat DB as described above (if support for same is compiled in).

       i)     If  the  string  contains  none  of  these  prefixes  but starts with a slash ("/")
              character, it is presumed to be a flat file as described above.

       j)     If the string begins with "csl:", the string is treated as a  comma-separated  list
              as described in m) below.

       k)     If  the  string begins with "erlang:", it is presumed to refer to a function called
              to be made to the specified distributed Erlang node(s). The specification is of the
              form

              erlang:node@host[,...]:cookie:module:function

              where  node[,...]   is a list of comma-separated erlang nodes, cookie is the cookie
              for the known nodes of the distributed Erlang setup, module  is  the  name  of  the
              Erlang  module where the function to be called resides, function is the name of the
              Erlang function to be called. For example, (all in one line):

              erlang:mynode@myhost,myothernode@myotherhost:
                     chocolate:dkim:lookup

              will join the distributed Erlang setup  connecting  to  either  "mynode@myhost"  or
              "myothernode@myotherhost"   (connections   to  nodes  are  tried  in  order)  using
              "chocolate" as the cookie, and use the function "dkim:lookup/1" for lookups.

       l)     If the string begins with "mdb:", it refers to a directory that contains  a  memory
              database, as provided by libmdb from OpenLDAP.

       m)     In  any  other case, the string is presumed to be a comma-separated list.  Elements
              in the list are either simple data elements that are part of the  set  or,  in  the
              case  of  an  entry  of  the form "x=y", are stored as key-value pairs as described
              above.

OPTIONS

       -A     Automatically re-start  on  failures.   Use  with  caution;  if  the  filter  fails
              instantly  after  it  starts,  this  can  cause  a tight fork(2) loop.  This can be
              mitigated using some values in the configuration file  to  limit  restarting.   See
              opendkim.conf(5).

       -b modes
              Selects  operating  modes.   modes  is  a concatenation of characters that indicate
              which mode(s) of  operation  are  desired.   Valid  modes  are  s  (signer)  and  v
              (verifier).  The default is sv except in test mode (see -t below) in which case the
              default is v.

       -c canon
              Selects the canonicalization method(s) to be  used  when  signing  messages.   When
              verifying,  the  message's  DKIM-Signature:  header  specifies the canonicalization
              method.  The recognized values are relaxed  and  simple  as  defined  by  the  DKIM
              specification.   The  default  is  simple.   The  value  may  include two different
              canonicalizations separated by a slash ("/") character, in  which  case  the  first
              will be applied to the headers and the second to the body.

       -d dataset
              A  set  of  domains  whose  mail  should be signed by this filter.  Mail from other
              domains will be verified rather than being signed.

       -D     Sign subdomains of those listed by the -d option as well as the actual domains.

       -e name
              Extracts the value of name from the configuration file (if any).

       -f     Normally opendkim forks and exits immediately, leaving the service running  in  the
              background.  This flag suppresses that behaviour so that it runs in the foreground.

       -F time
              Specifies a fixed time to use when generating signatures.  Ignored unless also used
              in conjunction with -t (see below).  The time must be expressed in the  usual  UNIX
              time_t (seconds since epoch) format.

       -k keyfile
              Gives  the  location  of  a  PEM-formatted  private  key to be used for signing all
              messages.  Ignored if a configuration file is referenced that defines a KeyTable.

       -l     Log via calls to syslog(3) any interesting activity.

       -L min[%+]
              Instructs the verification code to fail messages for which a partial signature  was
              received.   There  are three possible formats: min indicating at least min bytes of
              the message must be signed (or if the message is smaller than min then  all  of  it
              must  be  signed); min% requiring that at least min percent of the received message
              must be signed; and min+ meaning there may be no more than min  bytes  of  unsigned
              data appended to the message for it to be considered valid.

       -n     Parse  the  configuration  file  and  command  line arguments, reporting any errors
              found, and then exit.  The exit value will be  0  if  the  filter  would  start  up
              without complaint, or non-zero otherwise.

       -o dataset
              Specifies  a list of headers that should be omitted when generating signatures.  If
              an entry in the list names any header which is mandated by the DKIM  specification,
              the  entry  is  ignored.   A  set of headers is listed in the DKIM specification as
              "SHOULD NOT" be signed; the default list for this parameter contains those  headers
              (Return-Path,  Received,  Comments,  Keywords, Bcc, Resent-Bcc and DKIM-Signature).
              To omit no headers, simply use the string "-" (or any string  that  will  match  no
              headers).

       -p socketspec
              Specifies  the  socket  that  should  be  established  by  the  filter  to  receive
              connections from sendmail(8) in order to provide service.  socketspec is in one  of
              two  forms: local:path which creates a UNIX domain socket at the specified path, or
              inet:port[@host] or inet6:port[@host] which creates a TCP socket on  the  specified
              port  using  the  requested  protocol family.  If the host is not given as either a
              hostname or an IP address, the socket will  be  listening  on  all  interfaces.   A
              literal  IP address must be enclosed in square brackets.  If neither socket type is
              specified, local is assumed, meaning the parameter is  interpreted  as  a  path  at
              which  the socket should be created.  This parameter is mandatory either here or in
              the configuration file.

       -P pidfile
              Specifies a file into which the filter should write its process ID at startup.

       -Q     Query test mode.   The  filter  will  read  two  lines  from  standard  input,  one
              containing  a  database description to be opened and one containing a string of the
              form "q/n" where "q" is the query to be performed and "n" is the number  of  fields
              to be retrieved.

       -r     Checks  all  messages  for compliance with RFC5322 header count requirements.  Non-
              compliant messages are rejected.

       -s selector
              Defines the name of the selector to be used when signing messages.   See  the  DKIM
              specification for details.

       -S signalg
              Selects the signing algorithm to use when generating signatures.  Use 'opendkim -V'
              to see the list of supported algorithms.   The  default  is  rsa-sha256  if  it  is
              available, otherwise it will be rsa-sha1.

       -t testfiles
              Evaluates  (verifies)  one or more RFC5322-formatted message found in testfiles and
              exits.  The value of testfiles should be a comma-separated  list  of  one  or  more
              filenames,  one  of  which  may  be "-" if the message should be read from standard
              input.

       -T secs
              Sets the DNS timeout in seconds.  A value  of  0  causes  an  infinite  wait.   The
              default is 5.  Ignored if not using an asynchronous resolver package.  See also the
              NOTES section below.

       -u userid[:group]
              Attempts to be come the specified userid before starting operations.   The  process
              will  be assigned all of the groups and primary group ID of the named userid unless
              an alternate group is  specified.   See  the  FILE  PERMISSIONS  section  for  more
              information.

       -v     Increase  verbose  output  during  test mode (see -t above).  May be specified more
              than once to request increasing amounts of output.

       -V     Print the version number and supported canonicalization and  signature  algorithms,
              and then exit without doing anything else.

       -W     If  logging is enabled (see -l above), issues very detailed logging about the logic
              behind the filter's decision to either sign a message or verify it.  The "W" stands
              for  "Why?!"   since  the  logic  behind  the  decision  is  non-trivial and can be
              confusing to administrators not familiar with its operation.  A description of  how
              the  decision is made can be found in the OPERATION section of this document.  This
              causes a large increase in the amount of log data generated for each message, so it
              should be limited to debugging use and not enabled for general operation.

       -x configfile
              Read  the named configuration file.  See the opendkim.conf(5) man page for details.
              Values in the configuration file are overridden when their equivalents are provided
              on  the  command  line  until a configuration reload occurs.  The OPERATION section
              describes how reloads are triggered.  The default is to read a  configuration  file
              from  /etc/opendkim.conf  if  one  exists,  or  otherwise  to apply defaults to all
              values.

       -X     Tolerates  configuration  file  items  that  have   been   internally   marked   as
              "deprecated".  Normally when a configuration file item is removed from the package,
              it is flagged in this way for at least one full release cycle.  The presence  of  a
              deprecated  configuration  file item typically causes the filter to return an error
              and refuse to start.  Setting this flag will  allow  the  filter  to  start  and  a
              warning  is  logged.  In some future release when the item is removed completely, a
              different error results, and it will not be possible to start the filter.   Use  of
              this  flag  is  NOT  RECOMMENDED;  it  could effectively hide a major configuration
              change with serious security implications.

OPERATION

       A message will be verified unless it conforms to the signing criteria, which are: (1)  the
       domain  on  the From: address (if present) must be listed by the -d command line switch or
       the Domain configuration file setting, and (2) (a) the client connecting to the  MTA  must
       have  authenticated,  or  (b)  the client connecting to the MTA must be listed in the file
       referenced by the InternalHosts configuration file setting (or be in the default list  for
       that  option),  or  (c)  the  client  must be connected to a daemon port named by the MTAs
       configuration file setting, or (d) the MTA must have set one or more macros  matching  the
       criteria set by the MacroList configuration file setting.

       For  (a) above, the test is whether or not the MTA macro "{auth_type}" is set and contains
       any non-empty value.  This means the MTA must pass the value of that macro to  the  filter
       before or during the end-of-header (EOH) phase in order for its value to be tested.  Check
       your MTA's configuration documentation for details.

       For (1) above, other header fields may be selected using the  SenderHeaders  configuration
       file setting.  See opendkim.conf(5) for more information.

       When  signing  a  message, a DKIM-Signature: header will be prepended to the message.  The
       signature is computed using the private key provided.  You must be running  a  version  of
       sendmail(8) recent enough to be able to do header prepend operations (8.13.0 or later).

       When  verifying a message, an Authentication-Results: header will be prepended to indicate
       the presence of a signature and whether or not it could be validated against the  body  of
       the message using the public key advertised by the sender's nameserver.  The value of this
       header can be used by mail user agents to sort or discard messages that were not signed or
       could not be verified.

       Upon  receiving  SIGUSR1,  if the filter was started with a configuration file, it will be
       re-read and the new values used.  Note that any command line overrides provided at startup
       time  will  be lost when this is done.  Also, the following configuration file values (and
       their corresponding command line items, if any) are not  reloaded  through  this  process:
       AutoRestart  (-A),  AutoRestartCount,  AutoRestartRate,  Background,  MilterDebug, PidFile
       (-P), POPDBFile, Quarantine (-q), QueryCache, Socket (-p), StrictTestMode, TestPublicKeys,
       UMask,  UserID  (-u).   The filter does not automatically check the configuration file for
       changes and reload.

MTA MACROS

       opendkim makes use of three MTA-provided macros, plus any demanded by configuration.   The
       basic three are: "i" (the envelope ID, also known as the job ID or the queue ID), which is
       used for logging; "daemon_name" (the symbolic name given to the MTA instance that accepted
       the  connection), which is used when performing tests against any "MTAs" setting used; and
       "auth_type", which is used to determine whether or not the SMTP  client  authenticated  to
       the  MTA.  If the MTA does not provide them to opendkim then it is not able to apply their
       corresponding tests or do useful logging.  Consult your MTA documentation to determine how
       to adjust your its configuration if some or all of these are not available.

FILE PERMISSIONS

       When  the  filter  is  started  as  the superuser and the UserID (-u) setting is used, the
       filter gives up its root privileges by changing to the specified user after the  following
       steps  are  taken:  (1) the configuration file (if any) is loaded; (2) if the KeyFile (-k)
       setting is used, that key is loaded into memory; (3) all data sets  in  the  configuration
       file are opened, and those that are based on flat files are also read into memory; and (4)
       if ChangeRootDirectory is set, the process root is changed to that directory.  This  means
       on configuration reload, the filter will not be accessing these files or the configuration
       file as the superuser (and possibly from a different root), and any key  files  referenced
       by the KeyTable will also be accessed by the new user.

       Thus,  keys  referenced  by  the  KeyTable  must  always  be  accessible  for  read by the
       unprivileged user.  Also, run-time reloads are not possible if any of the other files will
       not be readable by the unprivileged user.

ENVIRONMENT

       The following environment variable(s) can be used to adjust the behaviour of this filter:

       DKIM_TMPDIR
              The directory to use when creating temporary files.  The default is /tmp.

NOTES

       When  using  DNS  timeouts (see the -T option above), be sure not to use a timeout that is
       larger than the timeout being used  for  interaction  between  sendmail  and  the  filter.
       Otherwise,  the MTA could abort a message while waiting for a reply from the filter, which
       in turn is still waiting for a DNS reply.

       The POP authentication database is expected to be a Sleepycat DB file (formerly known as a
       Berkeley  DB)  in  hash  format with keys containing the IP address in text form without a
       terminating NULL.  The values of these records are not checked; only the existence of such
       records  is  of  interest.   The  filter  will  attempt  to establish a shared lock on the
       database before reading from it, so any programs which write to the database  should  keep
       their  lock use to a minimum or else this filter will appear to hang while waiting for the
       lock operation to complete.

       Features that involve specification  of  IPv4  addresses  or  CIDR  blocks  will  use  the
       inet_addr(3)  function  to  parse that information.  Users should be familiar with the way
       that function handles the non-trivial cases (for example, "192.0.2/24" and  "192.0.2.0/24"
       are not the same thing).

EXIT STATUS

       Filter exit status codes are selected according to sysexits(3).

HISTORY

       DKIM  is  an amalgam of Yahoo!'s DomainKeys proposal, and Cisco's Internet Identified Mail
       (IIM) proposal.

VERSION

       This man page covers version 2.11.0 of opendkim.

COPYRIGHT

       Copyright (c) 2005-2008, Sendmail, Inc. and its suppliers.  All rights reserved.

       Copyright (c) 2009-2013, 2015, The Trusted Domain Project.  All rights reserved.

SEE ALSO

       opendkim.conf(5), sendmail(8)

       Sendmail Operations Guide

       RFC5321 - Simple Mail Transfer Protocol

       RFC5322 - Internet Messages

       RFC5451 - Message Header Field for Indicating Message Authentication Status

       RFC6008 - Authentication-Results  Registration  for  Differentiating  among  Cryptographic
       Results

       RFC6376 - DomainKeys Identified Mail

                                    The Trusted Domain Project                        opendkim(8)