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>