Ubuntu Manpage: dk-filter - DomainKeys filter for sendmail

Provided by: dk-filter_1.0.0.dfsg-1.2_amd64

NAME

       dk-filter - DomainKeys filter for sendmail

SYNOPSIS

       dk-filter  -p socketspec [-a peerlist] [-A] [-b modes] [-c canon] [-C config] [-d domains]
       [-D] [-f] [-i ilist] [-I eilist] [-h] [-H] [-k] [-l] [-m  mtas]  [-M  macro[=value][,...]]
       [-o  hdrlist]  [-P pidfile] [-q] [-R] [-s keyfile] [-S selector] [-T secs] [-u userid] [-U
       popdb] [-V]

DESCRIPTION

       dk-filter implements Yahoo!, Inc.'s DomainKeys draft standard for signing and verifying e-
       mail messages on a per-domain basis.

       Details regarding the protocol and other issues related to the draft standard can be found
       at http://antispam.yahoo.com/domainkeys.

OPTIONS

-a peerlist
Identifies a file of "peers" which identifies clients whose connections should be
accepted without processing by this filter. The peerlist should contain on each
line a hostname, domain name (e.g. ".example.com"), IP address, an IPv6 address
(including an IPv4 mapped address), or a CIDR-style IP specification (e.g.
"192.168.1.0/24").

-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.

-b modes
Selects operating modes. modes is a concatenation of characters which indicate
which mode(s) of operation are desired. Valid modes are s (signer) and v
(verifier). The default is sv.

-c canon
Selects the canonicalization method to be used when signing messages. When
verifying, the message's DomainKey-Signature: header specifies the canonicalization
method. The recognized values are nofws and simple as defined by the DomainKeys
draft. The default is simple.

-C config
Configuration control. See the CONFIGURATION section for details.

-d domain [,...]
A comma-separated list of domains whose mail should be signed by this filter. Mail
from other domains will be verified rather than being signed.

If the value of this parameter starts with a "/" character, it is assumed to be a
filename from which the domain list will be read, one per line, with "#" characters
indicating the beginning of a comment.

In either case, the domain name(s) may contain the special character "*" which is
treated as a wildcard character matching zero or more characters in a domain name.

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

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

-h Causes dk-filter to add a header indicating the presence of this filter in the path
of the message from injection to delivery. The product's name, version, and the
job ID are included in the header's contents.

-H Includes on DomainKey signatures the list of headers that were included in the
signature. This makes the signature header larger by explicitly listing the
included headers, but this also allows verifying agents to ignore headers that were
added in transit.

-i ilist
Identifies a file of internal hosts whose mail should be signed rather than
verified. Entries in this file follow the same form as those of the -a option
above. If not specified, the default of "127.0.0.1" is applied.

-I eilist
Identifies a file of "external" hosts which may send mail through the server as one
of the signing domains without credentials as such; basically suppresses the
"external host (hostname) tried to send mail as (domain)" log messages. Entries in
this file follow the same form as those of the -a option above.

-k Causes -s to be interpreted as the location of a key list, which is a file listing
rules for signing with multiple keys. The key list should contain a set of lines
of the form sender-pattern:keypath where sender-pattern is a pattern to match
against message senders (with the special character "*" interpreted as "zero or
more characters"), and keypath is the path to the PEM-formatted private key to be
used for signing messages which match the sender-pattern. The selector used in the
signature will be the filename portion of keypath.

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

-m mta [,...]
A comma-separated list of MTA names (a la the sendmail(8) DaemonPortOptions Name
parameter) whose mail should be signed by this filter. There is no default.

-M macro[=value][,...]
Defines a set of MTA-provided macros which should be checked to see if the sender
has been determined to be a local user and therefore whether or not the message
should be signed; if a value is specified, the value of the macro must match the
value specified (matching is case-insensitive), otherwise the macro must be defined
but may contain any value. The list is empty by default.

-o header [,...]
A comma-separated list of headers which should not be signed. Ignored when
verifying.

-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] which creates a TCP socket on the specified port. If the host is
not given as either a hostname or an IP address, the socket will be listening on
all interfaces. This option is mandatory.

-P pidfile
Writes the process ID of the filter, once started, to the filename given.

-q Requests that messages which fail verification be quarantined by the MTA.
(Requires a sufficiently recent version of the milter library.)

-R When a signature verification fails and the signing site advertises a reporting
address (i.e. r=user@host in its policy record), send a structured report to that
address containing details needed to reproduce the problem.

-s keyfile
Gives the location of a PEM-formatted private key to be used for message signing.

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

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

-u userid
Attempts to be come the specified userid before starting operations.

-U popdb
Requests that the filter consult a POP authentication database for IP addresses
that should be allowed for signing. The filter must be specially compiled to
enable this feature, since it adds a library dependency.

-V Print the version number and exit without doing anything else.

CONFIGURATION

       The value of the -C switch is a comma-separated list of settings of the form result=action
       which  defines what the filter should do with messages that produce certain results.  Each
       result and each action has a full name and  an  abbreviated  name.   Either  is  accepted.
       Below, the abbreviated name appears in parentheses.

       results
              badsignature  (bad)  the signature found in the message did not verify successfully
              against the message; dnserror (dns) an error was encountered attempting to retrieve
              a  public  key  from  the  nameserver;  internal  (int) an internal error occurred;
              nosignature (no) no signature was present on the message;  signaturemissing  (miss)
              no signature was present on the message which claims to sign all messages.

       action accept  (a) accept the message; discard (d) discard the message; tempfail (t) temp-
              fail the message; reject (r) reject the message.

       In the interests of minimal initial impact, the defaults for badsignature, nosignature and
       signaturemissing are all accept, and the default for the others is tempfail.

OPERATION

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

       When signing a message, a DomainKey-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.

ENVIRONMENT

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

       DK_TMPDIR
              The directory to use when creating temporary files.  The default is /var/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.

VERSION

       This man page covers version 1.0.0 of dk-filter.

COPYRIGHT

       Copyright (c) 2004-2008, Sendmail, Inc. and its suppliers.  All rights reserved.