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Mail::SpamAssassin::Plugin::DKIUser Contributed Perl DocumentaMail::SpamAssassin::Plugin::DKIM(3)

NAME
       Mail::SpamAssassin::Plugin::DKIM - perform DKIM verification tests

SYNOPSIS
	loadplugin Mail::SpamAssassin::Plugin::DKIM [/path/to/DKIM.pm]

       Taking into account signatures from any signing domains:

	full   DKIM_SIGNED	     eval:check_dkim_signed()
	full   DKIM_VALID	     eval:check_dkim_valid()
	full   DKIM_VALID_AU	     eval:check_dkim_valid_author_sig()

       Taking into account signatures from specified signing domains only: (quotes may be omitted
       on domain names consisting only of letters, digits, dots, and minus characters)

	full   DKIM_SIGNED_MY1	     eval:check_dkim_signed('dom1','dom2',...)
	full   DKIM_VALID_MY1	     eval:check_dkim_valid('dom1','dom2',...)
	full   DKIM_VALID_AU_MY1     eval:check_dkim_valid_author_sig('d1','d2',...)

	full   __DKIM_DEPENDABLE     eval:check_dkim_dependable()

       Author Domain Signing Practices (ADSP) from any author domains:

	header DKIM_ADSP_NXDOMAIN    eval:check_dkim_adsp('N')
	header DKIM_ADSP_ALL	     eval:check_dkim_adsp('A')
	header DKIM_ADSP_DISCARD     eval:check_dkim_adsp('D')
	header DKIM_ADSP_CUSTOM_LOW  eval:check_dkim_adsp('1')
	header DKIM_ADSP_CUSTOM_MED  eval:check_dkim_adsp('2')
	header DKIM_ADSP_CUSTOM_HIGH eval:check_dkim_adsp('3')

       Author Domain Signing Practices (ADSP) from specified author domains only:

	header DKIM_ADSP_MY1	     eval:check_dkim_adsp('*','dom1','dom2',...)

	describe DKIM_SIGNED   Message has a DKIM or DK signature, not necessarily valid
	describe DKIM_VALID    Message has at least one valid DKIM or DK signature
	describe DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain
	describe __DKIM_DEPENDABLE     A validation failure not attributable to truncation

	describe DKIM_ADSP_NXDOMAIN    Domain not in DNS and no valid author domain signature
	describe DKIM_ADSP_ALL	       Domain signs all mail, no valid author domain signature
	describe DKIM_ADSP_DISCARD     Domain signs all mail and suggests discarding mail with no valid author domain signature, no valid author domain signature
	describe DKIM_ADSP_CUSTOM_LOW  adsp_override is CUSTOM_LOW, no valid author domain signature
	describe DKIM_ADSP_CUSTOM_MED  adsp_override is CUSTOM_MED, no valid author domain signature
	describe DKIM_ADSP_CUSTOM_HIGH adsp_override is CUSTOM_HIGH, no valid author domain signature

       For compatibility with pre-3.3.0 versions, the following are synonyms:

	OLD: eval:check_dkim_verified = NEW: eval:check_dkim_valid
	OLD: eval:check_dkim_signall  = NEW: eval:check_dkim_adsp('A')
	OLD: eval:check_dkim_signsome = NEW: redundant, semantically always true

       The __DKIM_DEPENDABLE eval rule deserves an explanation. The rule yields true when
       signatures are supplied by a caller, OR ELSE when signatures are obtained by this plugin
       AND either there are no signatures OR a rule __TRUNCATED was false. In other words:
       __DKIM_DEPENDABLE is true when failed signatures can not be attributed to message
       truncation when feeding a message to SpamAssassin.  It can be consulted to prevent false
       positives on large but truncated messages with poor man's implementation of ADSP by hand-
       crafted rules.

DESCRIPTION
       This SpamAssassin plugin implements DKIM lookups as described by the RFC 4871, as well as
       historical DomainKeys lookups, as described by RFC 4870, thanks to the support for both
       types of signatures by newer versions of module Mail::DKIM.

       It requires the "Mail::DKIM" CPAN module to operate. Many thanks to Jason Long for that
       module.

TAGS
       The following tags are added to the set, available for use in reports, header fields,
       other plugins, etc.:

	 _DKIMIDENTITY_
	   Agent or User Identifier (AUID) (the 'i' tag) from valid signatures;

	 _DKIMDOMAIN_
	   Signing Domain Identifier (SDID) (the 'd' tag) from valid signatures;

       Identities and domains from signatures which failed verification are not included in these
       tags. Duplicates are eliminated (e.g. when there are two or more valid signatures from the
       same signer, only one copy makes it into a tag).  Note that there may be more than one
       signature in a message - currently they are provided as a space-separated list, although
       this behaviour may change.

SEE ALSO
       "Mail::DKIM", "Mail::SpamAssassin::Plugin"

	 http://jason.long.name/dkimproxy/
	 http://tools.ietf.org/rfc/rfc4871.txt
	 http://tools.ietf.org/rfc/rfc4870.txt
	 http://tools.ietf.org/rfc/rfc5617.txt
	 http://ietf.org/html.charters/dkim-charter.html

USER SETTINGS
       whitelist_from_dkim author@example.com [signing-domain]
	   Works similarly to whitelist_from, except that in addition to matching an author
	   address (From) to the pattern in the first parameter, the message must also carry a
	   Domain Keys Identified Mail (DKIM) signature made by a signing domain (SDID, i.e. the
	   d= tag) that is acceptable to us.

	   Only one whitelist entry is allowed per line, as in "whitelist_from_rcvd".  Multiple
	   "whitelist_from_dkim" lines are allowed. File-glob style characters are allowed for
	   the From address (the first parameter), just like with "whitelist_from_rcvd". The
	   second parameter does not accept wildcards.

	   If no signing-domain parameter is specified, the only acceptable signature will be an
	   Author Domain Signature (sometimes called first-party signature) which is a signature
	   where the signing domain (SDID) of a signature matches the domain of the author's
	   address (i.e. the address in a From header field).

	   Since this whitelist requires a DKIM check to be made, network tests must be enabled.

	   Examples of whitelisting based on an author domain signature (first-party):

	     whitelist_from_dkim joe@example.com
	     whitelist_from_dkim *@corp.example.com
	     whitelist_from_dkim *@*.example.com

	   Examples of whitelisting based on third-party signatures:

	     whitelist_from_dkim jane@example.net      example.org
	     whitelist_from_dkim rick@info.example.net example.net
	     whitelist_from_dkim *@info.example.net    example.net
	     whitelist_from_dkim *@*		       remailer.example.com

       def_whitelist_from_dkim author@example.com [signing-domain]
	   Same as "whitelist_from_dkim", but used for the default whitelist entries in the
	   SpamAssassin distribution.  The whitelist score is lower, because these are often
	   targets for abuse of public mailers which sign their mail.

       unwhitelist_from_dkim author@example.com [signing-domain]
	   Removes an email address with its corresponding signing-domain field from
	   def_whitelist_from_dkim and whitelist_from_dkim tables, if it exists.  Parameters to
	   unwhitelist_from_dkim must exactly match the parameters of a corresponding
	   whitelist_from_dkim or def_whitelist_from_dkim config option which created the entry,
	   for it to be removed (a domain name is matched case-insensitively);	i.e. if a
	   signing-domain parameter was specified in a whitelisting command, it must also be
	   specified in the unwhitelisting command.

	   Useful for removing undesired default entries from a distributed configuration by a
	   local or site-specific configuration or by "user_prefs".

       adsp_override domain [signing-practices]
	   Currently few domains publish their signing practices (RFC 5617 - ADSP), partly
	   because the ADSP rfc is rather new, partly because they think hardly any recipient
	   bothers to check it, and partly for fear that some recipients might lose mail due to
	   problems in their signature validation procedures or mail mangling by mailers beyond
	   their control.

	   Nevertheless, recipients could benefit by knowing signing practices of a sending
	   (author's) domain, for example to recognize forged mail claiming to be from certain
	   domains which are popular targets for phishing, like financial institutions.
	   Unfortunately, as signing practices are seldom published or are weak, it is hardly
	   justifiable to look them up in DNS.

	   To overcome this chicken-or-the-egg problem, the "adsp_override" mechanism allows
	   recipients using SpamAssassin to override published or defaulted ADSP for certain
	   domains. This makes it possible to manually specify a stronger (or weaker) signing
	   practices than a signing domain is willing to publish (explicitly or by default), and
	   also save on a DNS lookup.

	   Note that ADSP (published or overridden) is only consulted for messages which do not
	   contain a valid DKIM signature from the author's domain.

	   According to RFC 5617, signing practices can be one of the following: "unknown", "all"
	   and "discardable".

	   "unknown": The domain might sign some or all email - messages from the domain may or
	   may not have an Author Domain Signature. This is a default if a domain exists in DNS
	   but no ADSP record is found.

	   "all": All mail from the domain is signed with an Author Domain Signature.

	   "discardable": All mail from the domain is signed with an Author Domain Signature.
	   Furthermore, if a message arrives without a valid Author Domain Signature, the domain
	   encourages the recipient(s) to discard it.

	   ADSP lookup can also determine that a domain is "out of scope", i.e., the domain does
	   not exist (NXDOMAIN) in the DNS.

	   To override domain's signing practices in a SpamAssassin configuration file, specify
	   an "adsp_override" directive for each sending domain to be overridden.

	   Its first argument is a domain name. Author's domain is matched against it, matching
	   is case insensitive. This is not a regular expression or a file-glob style wildcard,
	   but limited wildcarding is still available: if this argument starts by a "*." (or is a
	   sole "*"), author's domain matches if it is a subdomain (to one or more levels) of the
	   argument. Otherwise (with no leading asterisk) the match must be exact (not a
	   subdomain).

	   An optional second parameter is one of the following keywords (case-insensitive):
	   "nxdomain", "unknown", "all", "discardable", "custom_low", "custom_med",
	   "custom_high".

	   Absence of this second parameter implies "discardable". If a domain is not listed by a
	   "adsp_override" directive nor does it explicitly publish any ADSP record, then
	   "unknown" is implied for valid domains, and "nxdomain" for domains not existing in
	   DNS. (Note: domain validity is only checked with versions of Mail::DKIM 0.37 or later
	   (actually since 0.36_5), the "nxdomain" would never turn up with older versions).

	   The strong setting "discardable" is useful for domains which are known to always sign
	   their mail and to always send it directly to recipients (not to mailing lists), and
	   are frequent targets of fishing attempts, such as financial institutions. The
	   "discardable" is also appropriate for domains which are known never to send any mail.

	   When a message does not contain a valid signature by the author's domain (the domain
	   in a From header field), the signing practices pertaining to author's domain determine
	   which of the following rules fire and contributes its score: DKIM_ADSP_NXDOMAIN,
	   DKIM_ADSP_ALL, DKIM_ADSP_DISCARD, DKIM_ADSP_CUSTOM_LOW, DKIM_ADSP_CUSTOM_MED,
	   DKIM_ADSP_CUSTOM_HIGH. Not more than one of these rules can fire for messages that
	   have one author (but see below). The last three can only result from a
	   'signing-practices' as given in a "adsp_override" directive (not from a DNS lookup),
	   and can serve as a convenient means of providing a different score if scores assigned
	   to DKIM_ADSP_ALL or DKIM_ADSP_DISCARD are not considered suitable for some domains.

	   RFC 5322 permits a message to have more than one author - multiple addresses may be
	   listed in a single From header field.  RFC 5617 defines that a message with multiple
	   authors has multiple signing domain signing practices, but does not prescribe how
	   these should be combined. In presence of multiple signing practices, more than one of
	   the DKIM_ADSP_* rules may fire.

	   As a precaution against firing DKIM_ADSP_* rules when there is a known local reason
	   for a signature verification failure, the domain's ADSP is considered 'unknown' when
	   DNS lookups are disabled or a DNS lookup encountered a temporary problem on fetching a
	   public key from the author's domain. Similarly, ADSP is considered 'unknown' when this
	   plugin did its own signature verification (signatures were not passed to SA by a
	   caller) and a metarule __TRUNCATED was triggered, indicating the caller intentionally
	   passed a truncated message to SpamAssassin, which was a likely reason for a signature
	   verification failure.

	   Example:

	     adsp_override *.mydomain.example.com   discardable
	     adsp_override *.neversends.example.com discardable

	     adsp_override ebay.com
	     adsp_override *.ebay.com
	     adsp_override ebay.co.uk
	     adsp_override *.ebay.co.uk
	     adsp_override paypal.com
	     adsp_override *.paypal.com
	     adsp_override amazon.com
	     adsp_override ealerts.bankofamerica.com
	     adsp_override americangreetings.com
	     adsp_override egreetings.com
	     adsp_override bluemountain.com
	     adsp_override hallmark.com   all
	     adsp_override *.hallmark.com all
	     adsp_override youtube.com	  custom_high
	     adsp_override google.com	  custom_low
	     adsp_override gmail.com	  custom_low
	     adsp_override googlemail.com custom_low
	     adsp_override yahoo.com	  custom_low
	     adsp_override yahoo.com.au   custom_low
	     adsp_override yahoo.se	  custom_low

	     adsp_override junkmailerkbw0rr.com nxdomain
	     adsp_override junkmailerd2hlsg.com nxdomain

	     # effectively disables ADSP network DNS lookups for all other domains:
	     adsp_override *		  unknown

	     score DKIM_ADSP_ALL	  2.5
	     score DKIM_ADSP_DISCARD	 25
	     score DKIM_ADSP_NXDOMAIN	  3

	     score DKIM_ADSP_CUSTOM_LOW   1
	     score DKIM_ADSP_CUSTOM_MED   3.5
	     score DKIM_ADSP_CUSTOM_HIGH  8

ADMINISTRATOR SETTINGS
       dkim_timeout n		  (default: 5)
	   How many seconds to wait for a DKIM query to complete, before scanning continues
	   without the DKIM result.

perl v5.16.3				    2011-06-06	      Mail::SpamAssassin::Plugin::DKIM(3)
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