.TH dkim-filter.conf 5 "Sendmail, Inc."

.SH NAME
.B dkim-filter.conf
- Configuration file for dkim-filter

.SH LOCATION
.I /etc/mail/dkim-filter.conf

.SH DESCRIPTION
.I dkim-filter(8)
implements the
.B DKIM
specification for signing and verifying e-mail messages on a per-domain
basis.  This file is its configuration file, read on startup only.

Blank lines are ignored.  Lines containing a hash ("#") character are
truncated at the hash character.

Other content should be the name of a parameter, followed by white space,
followed by the value of that parameter.

For parameters which are Boolean in nature, only the first byte of
the value is processed.  For positive values, the following are accepted:
"T", "t", "Y", "y", "1".  For negative values, the following are accepted:
"F", "f", "N", "n", "0".

Many, but not all, of these parameters are also available as command
line options to
.I dkim-filter(8).
However, new parameters are generally not added as command line options
so the complete set of options is available here, and thus use of the
configuration file is encouraged.  In some future release, the
set of available command line options is likely to get trimmed.

.SH PARAMETERS
.TP
.I AlwaysSignHeaders (string)
Specifies a list of headers which should be included in all signature
header lists (the "h=" tag) even if they were not present at the time
the signature was generated.  The string should be a comma-separated
list of header names.  The list is empty by default.  The purpose of
listing an absent header is to prevent its addition between the signer
and the verifier, since the verifier would include that header if it were
added when performing verification, which would mean the signed message
and the verified message were different and the verification would fail.

.TP
.I AutoRestart (Boolean)
Automatically re-start on failures.  Use with caution; if the filter
fails instantly after it starts, this can cause a tight
.I fork(2)
loop.

.TP
.I Background (Boolean)
Normally
.I dkim-filter
forks and exits immediately, leaving the service running in the background.
This flag suppresses that behaviour so that it runs in the foreground.

.TP
.I BodyLengths (Boolean)
Requests that
.I dkim-filter
include the "l=" body length tag when generating signatures.  This
indicates to the verifier that only a certain amount of the original
message was signed, allowing tolerance of things like mailing list
managers which append list-specific text to the end of mailings
it processes.  However, this also enables an abuse attack.  See the
DKIM specification for more information.

.TP
.I Canonicalization (string)
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
.I relaxed
and
.I simple
as defined by the DKIM specification.  The default is
.I 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.

.TP
.I ClockDrift (integer)
Sets the tolerance in seconds to be applied when determining whether a
signature was either expired or generated in the future.  The default
is 300.

.TP
.I Diagnostics (Boolean)
Requests the inclusion of "z=" tags in signatures, which encode the
original header set for use by verifiers when diagnosing verification
failures.  Not recommended for normal operation.

.TP
.I DNSTimeout (integer)
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.

.TP
.I Domain (string)
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.

The value of this parameter may also be a filename from which domain names
will be read.  The "#" character in such a file is assumed to indicate a
comment.  An absolute path must be used (i.e. the first character must be
a "/").

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.

.TP
.I ExternalIgnoreList (string)
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 the file should be of the same form as those of
the
.I PeerList
option below.  The list is empty by default.

.TP
.I KeyFile (string)
Gives the location of a PEM-formatted private key to be used for signing
all messages.  Ignored if
.I KeyList
is defined.

.TP
.I KeyList (string)
Gives the location of a file listing rules for signing with multiple keys.
If present, overrides any
.I KeyFile
setting in the conifguration file.  The file named here should contain a
set of lines of the form
.I sender-pattern:signing-domain:keypath
where
.I sender-pattern
is a pattern to match against message senders (with the special character
"*" interpreted as "zero or more characters"),
.I signing-domain
is the domain to announce as the signing domain when generating signatures, and
.I keypath
is the path to the PEM-formatted private key to be used for signing messages
which match the
.I sender-pattern.
The selector used in the signature will be the filename portion of
.I keypath.
If the file referenced by
.I keypath
cannot be opened, the filter will try again by appending ".pem"
and then ".private" before giving up.

.TP
.I InternalHosts (string)
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
.I PeerList
option below.  If not specified, the default of "127.0.0.1" is applied.

.TP
.I MacroList (string)
Defines a set of MTA-provided
.I 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
.I value
is specified, the value of the macro must match a value specified
(matching is case-sensitive), otherwise the macro must be defined
but may contain any value.  The set is empty by default.  The general
format of the string is
.I test1[,test2[,...]]
where a "test" is of the form
.I macro[=value1[|value2[|...]]];
if one or more value is defined then the macro must be set to one of the
listed values, otherwise the macro must be set but can contain any
value.

.TP
.I MaximumHeaders (integer)
Defines the maximum number of bytes the header block of a message may
consume before the filter will reject the message.  This mitigates
a denial-of-service attack in which a client connects to the MTA
and begins feeding an unbounded number of header fields of arbitrary
size; since the filter keeps a cache of these, the attacker could
cause the filter to allocate an unspecified amount of memory.  The
default is 65536; a value of 0 removes the limit.

.TP
.I MaximumSignedBytes (integer)
Specifies the maximum number of bytes of message body to be signed.
Messages shorter than this limit will be signed in their entirety.
Setting this value forces
.I BodyLengths
to be "True".

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

.TP
.I Mode (string)
Selects operating modes.  The string is a concatenation of characters which
indicate which mode(s) of operation are desired.  Valid modes are
.I s
(signer) and
.I v
(verifier).  The default is
.I sv
except in test mode (see the
.I dkim-filter(8)
man page)
in which case the default is
.I v.

.TP
.I MTA (string)
A comma-separated list of MTA names (a la the
.I sendmail(8)
DaemonPortOptions Name parameter) whose mail should be signed by this
filter.  There is no default.

.TP
.I OmitHeaders (string)
Specifies a list of headers which should be omitted when generating
signatures.  The string should be a comma-separated list of header names.
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 which will match no headers).

.TP
.I On-BadSignature (string)
Selects the action to be taken when a signature fails to validate.
Possible values (with abbreviated forms in parentheses):
.I accept
(a) accept the message;
.I discard
(d) discard the message;
.I tempfail
(t) temp-fail the message;
.I reject
(r) reject the message.
The default is
.I accept.

.TP
.I On-Default (string)
Selects the action to be taken when any verification or internal error of
any kind is encountered.  This is processed before the other "On-" values
so it can be used as a blanket setting followed by specific overrides.

.TP
.I On-DNSError (string)
Selects the action to be taken when a transient DNS error is encountered.
Possible values are the same as those for
.I On-BadSignature.
The default is
.I tempfail.

.TP
.I On-InternalError (string)
Selects the action to be taken when an internal error of some kind is
encountered.  Possible values are the same as those for
.I On-BadSignature.
The default is
.I tempfail.

.TP
.I On-NoSignature (string)
Selects the action to be taken when a message arrives unsigned.
Possible values are the same as those for
.I On-BadSignature.
The default is
.I accept.

.TP
.I On-Security (string)
Selects the action to be taken when a message arrives containing properties
that may be a security concern.  Possible values are the same as those for
.I On-BadSignature.
The default is
.I tempfail.

.TP
.I On-SignatureMissing (string)
Selects the action to be taken when a message arrives unsigned from a domain
which advertises a "we sign everything" policy.  Possible values are the
same as those for
.I On-BadSignature.
The default is
.I accept.

.TP
.I PeerList (string)
Identifies a file of "peers" which identifies clients whose connections
should be accepted without processing by this filter.  The file
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").  An entry beginning
with a bang ("!") character means "not", allowing exclusions of specific
hosts that are otherwise members of larger sets.  The order of entries
in this file is therefore significant.

.TP
.I PidFile (string)
Specifies the path to a file which should be created at process start
containing the process ID.

.TP
.I POPDBFile (string)
Requests that the filter consult a POP authentication database named
in the string for IP addresses that should be allowed for signing.  The
filter must be compiled with the POPAUTH flag to enable this feature, since
it adds a library dependency.

.TP
.I Quarantine (Boolean)
Requests that messages which fail verification be quarantined by the
MTA.  (Requires a sufficiently recent version of the milter library.)

.TP
.I QueryCache (Boolean)
Instructs the DKIM library to maintain its own local cache of keys and
policies retrieved from DNS, rather than relying on the nameserver for
caching service.  Useful if the nameserver being used by the filter is
not local.  The filter must be compiled with the QUERY_CACHE flag to enable
this feature, since it adds a library dependency.

.TP
.I RemoveARAll (Boolean)
Removes all Authentication-Results: header fields which also satisfy the
requirements of
.I RemoveARFrom
below.  By default, only those containing a DKIM result are removed.

.TP
.I RemoveARFrom (string)
Lists patterns of hostnames whose Authentication-Results: header fields should
be removed before the message is passed for delivery.  By default only
those headers matching the local host's canonical name will be removed.
If more than one pattern is desired, the list should be comma-separated.
Matching is only done on full hostnames (e.g. "host.example.com") or on
domain names (e.g. ".example.com").

.TP
.I RemoveOldSignatures (Boolean)
Removes all existing signatures when operating in signing mode.

.TP
.I SignHeaders (string)
Specifies the list of headers which should be included when generating
signatures.  The string should be a comma-separated list of header names.
If the list omits any header which is mandated by the DKIM specification,
those headers are implicitly added.  By default, all headers present at the
time of signing except those which the DKIM specification says "SHOULD NOT"
be signed will be included when generating the signature.  See the
.I OmitHeaders
configuration option for more information.

.TP
.I Selector (string)
Defines the name of the selector to be used when signing messages.
See the
.B DKIM
specification for details.  Used only when signing with a single key;
see the
.I KeyList
parameter above for more information.

.TP
.I SendReports (Boolean)
If true, when a signature verification fails and the signing site advertises a
reporting address (i.e.
.I r=user@host
in its policy record), the filter will send a structured report to that
address containing details needed to reproduce the problem.

.TP
.I SignatureAlgorithm (string)
Selects the signing algorithm to use when generating signatures.
If the filter was compiled against version 0.9.8 or later of
.B OpenSSL
then both
.I rsa-sha1
and 
.I rsa-sha256
are available and the latter is the default.  Otherwise, only the former
is available and it is (obviously) the default.

.TP
.I SignatureTTL (integer)
Sets the time-to-live, in seconds, of signatures generated by the filter.
If not set, no expiration time is added to signatures.

.TP
.I Socket (string)
Specifies the socket that should be established by the filter to receive
connections from
.I sendmail(8)
in order to provide service.
.I socketspec
is in one of two forms:
.I local:path
which creates a UNIX domain socket at the specified
.I path,
or
.I inet:port[@host]
which creates a TCP socket on the specified
.I port.
If the
.I host
is not given as either a hostname or an IP address, the socket will be
listening on all interfaces.  This option is mandatory either in the
configuration file or on the command line.

.TP
.I StrictTestMode (Boolean)
Selects strict CRLF mode during testing (see the
.I -t
command line flag in the
.I dkim-filter(8)
man page); messages for which all header fields and body lines are not
CRLF-terminated are considered malformed and will produce an error.

.TP
.I SubDomains (Boolean)
Sign subdomains of those listed by the
.I Domain
parameter as well as the actual domains.

.TP
.I Syslog (Boolean)
Log via calls to
.I syslog(3)
any interesting activity.

.TP
.I SyslogSuccess (Boolean)
Log via calls to
.I syslog(3)
additional entries indicating successful signing or verification of
messages.

.TP
.I TestPublicKeys (string)
Names a file from which public keys should be read.  Intended for use only
during automated testing.

.TP
.I UMask (integer)
Requests a specific permissions mask to be used for file creation.
This only really applies to creation of the socket when
.I Socket
specifies a UNIX domain socket, and to the
.I PidFile
(if any); temporary files are created by the
.I mkstemp(3)
function which enforces a specific file mode on creation regardless
of the process umask.  See
.I umask(2)
for more information.

.TP
.I UserID (string)
Attempts to become the specified userid before starting operations.
The value is of the form
.I userid[:group].
The process will be assigned all of the groups and primary group ID of
the named
.I userid
unless an alternate
.I group
is specified.

.TP
.I UseSSPDeny (Boolean)
If "true", requests rejection of messages which are determined to be
"suspicious" according to the sending domain's published signing procedure
(SSP) record if that record also recommends rejection of such messages.
This does not apply if the SSP record advertises that the policy is in test.

.TP
.I X-Header (Boolean)
Causes
.I dkim-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.

.SH NOTES
When using DNS timeouts (see the
.I DNSTimeout
option above), be sure not to use a timeout that is larger than the timeout
being used for interaction between
.I 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.

.SH VERSION
This man page covers version 2.4.1 of
.I dkim-filter.

.SH COPYRIGHT
Copyright (c) 2007, Sendmail, Inc. and its suppliers.  All rights
reserved.

.SH SEE ALSO
.I dkim-filter(8), sendmail(8)
.P
RFC4871 - DomainKeys Identified Mail
.P
Authentication-Results Internet Draft