Mail::SpamAssassin::PlUser:Contributed PerMail::SpamAssassin::Plugin::DKIM(3p)



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 v5.12.2                      2011-06-Mail::SpamAssassin::Plugin::DKIM(3p)
