1Mail::SpamAssassin::PluUgsienr::CDoKnItMr(i3b)uted PerlMDaoiclu:m:eSnptaamtAisosnassin::Plugin::DKIM(3)
2
6 Mail::SpamAssassin::Plugin::DKIM - perform DKIM verification tests
7
9 loadplugin Mail::SpamAssassin::Plugin::DKIM [/path/to/DKIM.pm]
10 Taking into account signatures from any signing domains:
12 full DKIM_SIGNED eval:check_dkim_signed()
14 full DKIM_VALID eval:check_dkim_valid()
15 full DKIM_VALID_AU eval:check_dkim_valid_author_sig()
16 full DKIM_VALID_EF eval:check_dkim_valid_envelopefrom()
17 Taking into account ARC signatures (Authenticated Received Chain, RFC
19 8617) from any signing domains:
20 full ARC_SIGNED eval:check_arc_signed()
22 full ARC_VALID eval:check_arc_valid()
23 Taking into account signatures from specified signing domains only:
25 (quotes may be omitted on domain names consisting only of letters,
26 digits, dots, and minus characters)
27 full DKIM_SIGNED_MY1 eval:check_dkim_signed('dom1','dom2',...)
29 full DKIM_VALID_MY1 eval:check_dkim_valid('dom1','dom2',...)
30 full DKIM_VALID_AU_MY1 eval:check_dkim_valid_author_sig('d1','d2',...)
31 full __DKIM_DEPENDABLE eval:check_dkim_dependable()
33 Author Domain Signing Practices (ADSP) from any author domains:
35 header DKIM_ADSP_NXDOMAIN eval:check_dkim_adsp('N')
37 header DKIM_ADSP_ALL eval:check_dkim_adsp('A')
38 header DKIM_ADSP_DISCARD eval:check_dkim_adsp('D')
39 header DKIM_ADSP_CUSTOM_LOW eval:check_dkim_adsp('1')
40 header DKIM_ADSP_CUSTOM_MED eval:check_dkim_adsp('2')
41 header DKIM_ADSP_CUSTOM_HIGH eval:check_dkim_adsp('3')
42 Author Domain Signing Practices (ADSP) from specified author domains
44 only:
45 header DKIM_ADSP_MY1 eval:check_dkim_adsp('*','dom1','dom2',...)
47 describe DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid
49 describe DKIM_VALID Message has at least one valid DKIM or DK signature
50 describe DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain
51 describe DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain
52 describe __DKIM_DEPENDABLE A validation failure not attributable to truncation
53 describe DKIM_ADSP_NXDOMAIN Domain not in DNS and no valid author domain signature
55 describe DKIM_ADSP_ALL Domain signs all mail, no valid author domain signature
56 describe DKIM_ADSP_DISCARD Domain signs all mail and suggests discarding mail with no valid author domain signature, no valid author domain signature
57 describe DKIM_ADSP_CUSTOM_LOW adsp_override is CUSTOM_LOW, no valid author domain signature
58 describe DKIM_ADSP_CUSTOM_MED adsp_override is CUSTOM_MED, no valid author domain signature
59 describe DKIM_ADSP_CUSTOM_HIGH adsp_override is CUSTOM_HIGH, no valid author domain signature
60 For compatibility with pre-3.3.0 versions, the following are synonyms:
62 OLD: eval:check_dkim_verified = NEW: eval:check_dkim_valid
64 OLD: eval:check_dkim_signall = NEW: eval:check_dkim_adsp('A')
65 OLD: eval:check_dkim_signsome = NEW: redundant, semantically always true
66 The __DKIM_DEPENDABLE eval rule deserves an explanation. The rule
68 yields true when signatures are supplied by a caller, OR ELSE when
69 signatures are obtained by this plugin AND either there are no
70 signatures OR a rule __TRUNCATED was false. In other words:
71 __DKIM_DEPENDABLE is true when failed signatures can not be attributed
72 to message truncation when feeding a message to SpamAssassin. It can
73 be consulted to prevent false positives on large but truncated messages
74 with poor man's implementation of ADSP by hand-crafted rules.
75
77 This SpamAssassin plugin implements DKIM lookups as described by the
78 RFC 4871, as well as historical DomainKeys lookups, as described by RFC
79 4870, thanks to the support for both types of signatures by newer
80 versions of module Mail::DKIM.
81 It requires the "Mail::DKIM" CPAN module to operate. Many thanks to
83 Jason Long for that module.
84
86 The following tags are added to the set, available for use in reports,
87 header fields, other plugins, etc.:
88 _DKIMIDENTITY_
90 Agent or User Identifier (AUID) (the 'i' tag) from valid signatures;
91 _DKIMDOMAIN_
93 Signing Domain Identifier (SDID) (the 'd' tag) from valid signatures;
94 _DKIMSELECTOR_
96 DKIM selector (the 's' tag) from valid signatures;
97 Identities and domains from signatures which failed verification are
99 not included in these tags. Duplicates are eliminated (e.g. when there
100 are two or more valid signatures from the same signer, only one copy
101 makes it into a tag). Note that there may be more than one signature
102 in a message - currently they are provided as a space-separated list,
103 although this behaviour may change.
104
106 "Mail::DKIM" Mail::SpamAssassin::Plugin(3)
107 http://dkimproxy.sourceforge.net/
109 https://tools.ietf.org/rfc/rfc4871.txt
110 https://tools.ietf.org/rfc/rfc4870.txt
111 https://tools.ietf.org/rfc/rfc5617.txt
112 https://datatracker.ietf.org/group/dkim/about/
113
115 welcomelist_from_dkim author@example.com [signing-domain]
116 Previously whitelist_from_dkim which will work interchangeably
117 until 4.1.
118 Works similarly to welcomelist_from, except that in addition to
120 matching an author address (From) to the pattern in the first
121 parameter, the message must also carry a valid Domain Keys
122 Identified Mail (DKIM) signature made by a signing domain (SDID,
123 i.e. the d= tag) that is acceptable to us.
124 Only one welcomelist entry is allowed per line, as in
126 "welcomelist_from_rcvd". Multiple "welcomelist_from_dkim" lines
127 are allowed. File-glob style characters are allowed for the From
128 address (the first parameter), just like with
129 "welcomelist_from_rcvd".
130 The second parameter (the signing-domain) does not accept full
132 file-glob style wildcards, although a simple '*.' (or just a '.')
133 prefix to a domain name is recognized and implies any subdomain of
134 the specified domain (but not the domain itself).
135 If no signing-domain parameter is specified, the only acceptable
137 signature will be an Author Domain Signature (sometimes called
138 first-party signature) which is a signature where the signing
139 domain (SDID) of a signature matches the domain of the author's
140 address (i.e. the address in a From header field).
141 Since this welcomelist requires a DKIM check to be made, network
143 tests must be enabled.
144 Examples of welcomelisting based on an author domain signature
146 (first-party):
147 welcomelist_from_dkim joe@example.com
149 welcomelist_from_dkim *@corp.example.com
150 welcomelist_from_dkim *@*.example.com
151 Examples of welcomelisting based on third-party signatures:
153 welcomelist_from_dkim jane@example.net example.org
155 welcomelist_from_dkim rick@info.example.net example.net
156 welcomelist_from_dkim *@info.example.net example.net
157 welcomelist_from_dkim *@* mail7.remailer.example.com
158 welcomelist_from_dkim *@* *.remailer.example.com
159 def_welcomelist_from_dkim author@example.com [signing-domain]
161 Previously def_whitelist_from_dkim which will work interchangeably
162 until 4.1.
163 Same as "welcomelist_from_dkim", but used for the default
165 welcomelist entries in the SpamAssassin distribution. The
166 welcomelist score is lower, because these are often targets for
167 abuse of public mailers which sign their mail.
168 unwelcomelist_from_dkim author@example.com [signing-domain]
170 Previously unwhitelist_from_dkim which will work interchangeably
171 until 4.1.
172 Removes an email address with its corresponding signing-domain
174 field from def_welcomelist_from_dkim and welcomelist_from_dkim
175 tables, if it exists. Parameters to unwelcomelist_from_dkim must
176 exactly match the parameters of a corresponding
177 welcomelist_from_dkim or def_welcomelist_from_dkim config option
178 which created the entry, for it to be removed (a domain name is
179 matched case-insensitively); i.e. if a signing-domain parameter
180 was specified in a welcomelisting command, it must also be
181 specified in the unwelcomelisting command.
182 Useful for removing undesired default entries from a distributed
184 configuration by a local or site-specific configuration or by
185 "user_prefs".
186 adsp_override domain [signing-practices]
188 Currently few domains publish their signing practices (RFC 5617 -
189 ADSP), partly because the ADSP rfc is rather new, partly because
190 they think hardly any recipient bothers to check it, and partly for
191 fear that some recipients might lose mail due to problems in their
192 signature validation procedures or mail mangling by mailers beyond
193 their control.
194 Nevertheless, recipients could benefit by knowing signing practices
196 of a sending (author's) domain, for example to recognize forged
197 mail claiming to be from certain domains which are popular targets
198 for phishing, like financial institutions. Unfortunately, as
199 signing practices are seldom published or are weak, it is hardly
200 justifiable to look them up in DNS.
201 To overcome this chicken-or-the-egg problem, the "adsp_override"
203 mechanism allows recipients using SpamAssassin to override
204 published or defaulted ADSP for certain domains. This makes it
205 possible to manually specify a stronger (or weaker) signing
206 practices than a signing domain is willing to publish (explicitly
207 or by default), and also save on a DNS lookup.
208 Note that ADSP (published or overridden) is only consulted for
210 messages which do not contain a valid DKIM signature from the
211 author's domain.
212 According to RFC 5617, signing practices can be one of the
214 following: "unknown", "all" and "discardable".
215 "unknown": The domain might sign some or all email - messages from
217 the domain may or may not have an Author Domain Signature. This is
218 a default if a domain exists in DNS but no ADSP record is found.
219 "all": All mail from the domain is signed with an Author Domain
221 Signature.
222 "discardable": All mail from the domain is signed with an Author
224 Domain Signature. Furthermore, if a message arrives without a
225 valid Author Domain Signature, the domain encourages the
226 recipient(s) to discard it.
227 ADSP lookup can also determine that a domain is "out of scope",
229 i.e., the domain does not exist (NXDOMAIN) in the DNS.
230 To override domain's signing practices in a SpamAssassin
232 configuration file, specify an "adsp_override" directive for each
233 sending domain to be overridden.
234 Its first argument is a domain name. Author's domain is matched
236 against it, matching is case insensitive. This is not a regular
237 expression or a file-glob style wildcard, but limited wildcarding
238 is still available: if this argument starts by a "*." (or is a sole
239 "*"), author's domain matches if it is a subdomain (to one or more
240 levels) of the argument. Otherwise (with no leading asterisk) the
241 match must be exact (not a subdomain).
242 An optional second parameter is one of the following keywords
244 (case-insensitive): "nxdomain", "unknown", "all", "discardable",
245 "custom_low", "custom_med", "custom_high".
246 Absence of this second parameter implies "discardable". If a domain
248 is not listed by a "adsp_override" directive nor does it explicitly
249 publish any ADSP record, then "unknown" is implied for valid
250 domains, and "nxdomain" for domains not existing in DNS. (Note:
251 domain validity is only checked with versions of Mail::DKIM 0.37 or
252 later (actually since 0.36_5), the "nxdomain" would never turn up
253 with older versions).
254 The strong setting "discardable" is useful for domains which are
256 known to always sign their mail and to always send it directly to
257 recipients (not to mailing lists), and are frequent targets of
258 fishing attempts, such as financial institutions. The "discardable"
259 is also appropriate for domains which are known never to send any
260 mail.
261 When a message does not contain a valid signature by the author's
263 domain (the domain in a From header field), the signing practices
264 pertaining to author's domain determine which of the following
265 rules fire and contributes its score: DKIM_ADSP_NXDOMAIN,
266 DKIM_ADSP_ALL, DKIM_ADSP_DISCARD, DKIM_ADSP_CUSTOM_LOW,
267 DKIM_ADSP_CUSTOM_MED, DKIM_ADSP_CUSTOM_HIGH. Not more than one of
268 these rules can fire for messages that have one author (but see
269 below). The last three can only result from a 'signing-practices'
270 as given in a "adsp_override" directive (not from a DNS lookup),
271 and can serve as a convenient means of providing a different score
272 if scores assigned to DKIM_ADSP_ALL or DKIM_ADSP_DISCARD are not
273 considered suitable for some domains.
274 RFC 5322 permits a message to have more than one author - multiple
276 addresses may be listed in a single From header field. RFC 5617
277 defines that a message with multiple authors has multiple signing
278 domain signing practices, but does not prescribe how these should
279 be combined. In presence of multiple signing practices, more than
280 one of the DKIM_ADSP_* rules may fire.
281 As a precaution against firing DKIM_ADSP_* rules when there is a
283 known local reason for a signature verification failure, the
284 domain's ADSP is considered 'unknown' when DNS lookups are disabled
285 or a DNS lookup encountered a temporary problem on fetching a
286 public key from the author's domain. Similarly, ADSP is considered
287 'unknown' when this plugin did its own signature verification
288 (signatures were not passed to SA by a caller) and a metarule
289 __TRUNCATED was triggered, indicating the caller intentionally
290 passed a truncated message to SpamAssassin, which was a likely
291 reason for a signature verification failure.
292 Example:
294 adsp_override *.mydomain.example.com discardable
296 adsp_override *.neversends.example.com discardable
297 adsp_override ebay.com
299 adsp_override *.ebay.com
300 adsp_override ebay.co.uk
301 adsp_override *.ebay.co.uk
302 adsp_override paypal.com
303 adsp_override *.paypal.com
304 adsp_override amazon.com
305 adsp_override ealerts.bankofamerica.com
306 adsp_override americangreetings.com
307 adsp_override egreetings.com
308 adsp_override bluemountain.com
309 adsp_override hallmark.com all
310 adsp_override *.hallmark.com all
311 adsp_override youtube.com custom_high
312 adsp_override google.com custom_low
313 adsp_override gmail.com custom_low
314 adsp_override googlemail.com custom_low
315 adsp_override yahoo.com custom_low
316 adsp_override yahoo.com.au custom_low
317 adsp_override yahoo.se custom_low
318 adsp_override junkmailerkbw0rr.com nxdomain
320 adsp_override junkmailerd2hlsg.com nxdomain
321 # effectively disables ADSP network DNS lookups for all other domains:
323 adsp_override * unknown
324 score DKIM_ADSP_ALL 2.5
326 score DKIM_ADSP_DISCARD 25
327 score DKIM_ADSP_NXDOMAIN 3
328 score DKIM_ADSP_CUSTOM_LOW 1
330 score DKIM_ADSP_CUSTOM_MED 3.5
331 score DKIM_ADSP_CUSTOM_HIGH 8
332 dkim_minimum_key_bits n (default: 1024)
334 The smallest size of a signing key (in bits) for a valid signature
335 to be considered for welcomelisting. Additionally, the eval
336 function check_dkim_valid() will return false on short keys when
337 called with explicitly listed domains, and the eval function
338 check_dkim_valid_author_sig() will return false on short keys
339 (regardless of its arguments). Setting the option to 0 disables a
340 key size check.
341 Note that the option has no effect when the eval function
343 check_dkim_valid() is called with no arguments (like in a rule
344 DKIM_VALID). A mere presence of some valid signature on a message
345 has no reputational value (without being associated with a
346 particular domain), regardless of its key size - anyone can prepend
347 its own signature on a copy of some third party mail and re-send
348 it, which makes it no more trustworthy than without such signature.
349 This is also a reason for a rule DKIM_VALID to have a near-zero
350 score, i.e. a rule hit is only informational. This option is
351 evaluated on ARC signatures checks as well.
352
354 dkim_timeout n (default: 5)
355 How many seconds to wait for a DKIM query to complete, before
356 scanning continues without the DKIM result. A numeric value is
357 optionally suffixed by a time unit (s, m, h, d, w, indicating
358 seconds (default), minutes, hours, days, weeks).
359perl v5.38.0 2023-07-22Mail::SpamAssassin::Plugin::DKIM(3)