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.