Ubuntu Manpage: dkimpy - DKIM signing and verifying filter for MTAs

NAME

       dkimpy - DKIM signing and verifying filter for MTAs

SYNOPSIS

       dkimpy-milter [configfile]

DESCRIPTION

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

       dkimpy-milter 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.

DATA SETS

Many of the 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 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. Not all these datasets are currently used by dkimpy-milter. See dkimpy-
milter.conf(5) for details about specific options and which dataset types they use.

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.

i) If the string contains none of these prefixes but starts with a slash ("/") character, or "./" or
"../", it is presumed to be a flat file as described above. Note: In OpenDKIM "./" and "../" only
apply to KeyTable, but for dkimpy-milter it is generally applicable and KeyTable specification is
not a special case.

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

l) If the string begins with "mdb:", it refers to a directory that contains a memory database, as
provided by libmdb from OpenLDAP. [Not implemented yet]

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

       See    dkimpy-milter.conf  (5)  for  information  about  available  options.   Unlike  OpenDKIM, with the
              exception of -P for the pidfile and specifying the configuration file to use,  dkimpy-milter  does
              not support command line option switches.

              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.

FILE PERMISSIONS

       When the filter is started as the superuser and the UserID 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 or KeyFileEd25519 settings are used, the keys are 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 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.

       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 1.1.0 of dkimpy-milter.

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.

       Copyright (c) 2018, 2019 Scott Kitterman <scott@kitterman.com>