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opendkim.conf(5) File Formats Manual opendkim.conf(5) NAME opendkim.conf - Configuration file for opendkim LOCATION /usr/local/etc/opendkim.conf DESCRIPTION opendkim(8) implements the DKIM specification for signing and verifying e- mail messages on a per-domain basis. This file is its configuration file. Blank lines are ignored. Lines containing a hash ("#") character are trun- cated at the hash character to allow for comments in the file. Other content should be the name of a parameter, followed by white space, followed by the value of that parameter, each on a separate line. Parame- ter names are matched case-insensitively. For parameters that 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 opendkim(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. See the opendkim(8) man page for details about how and when the configura- tion file contents are reloaded. Some of these parameters are listed as having a type of "dataset". See the opendkim(8) man page for a description of such parameters. Unless otherwise stated, Boolean values default to "false", integer values default to 0, and string and dataset values default to being undefined. PARAMETERS AllowSHA1Only (Boolean) Permit verify mode when only SHA1 support is available. RFC6376 re- quires that verifiers implement both SHA1 and SHA256 support. Set- ting this feature changes the absence of SHA256 support from an er- ror to a warning. AlwaysAddARHeader (Boolean) Add an "Authentication-Results:" header field even to unsigned mes- sages from domains with no "signs all" policy. The reported DKIM result will be "none" in such cases. Normally unsigned mail from non-strict domains does not cause the results header field to be added. AuthservID (string) Sets the "authserv-id" to use when generating the Authentication-Re- sults: header field after verifying a message. The default is to use the name of the MTA processing the message. If the string "HOSTNAME" is provided, the name of the host running the filter (as returned by the gethostname(3) function) will be used. AuthservIDWithJobID (Boolean) If "true", requests that the authserv-id portion of the added Au- thentication-Results: header fields contain the job ID of the mes- sage being evaluated. AutoRestart (Boolean) Automatically re-start on failures. Use with caution; if the filter fails instantly after it starts, this can cause a tight fork(2) loop. AutoRestartCount (integer) Sets the maximum automatic restart count. After this number of au- tomatic restarts, the filter will give up and terminate. A value of 0 implies no limit; this is the default. AutoRestartRate (string) Sets the maximum automatic restart rate. If the filter begins restarting faster than the rate defined here, it will give up and terminate. This is a string of the form n/t[u] where n is an inte- ger limiting the count of restarts in the given interval and t[u] defines the time interval through which the rate is calculated; t is an integer and u defines the units thus represented ("s" or "S" for seconds, the default; "m" or "M" for minutes; "h" or "H" for hours; "d" or "D" for days). For example, a value of "10/1h" limits the restarts to 10 in one hour. There is no default, meaning restart rate is not limited. Background (Boolean) Causes opendkim to fork and exits immediately, leaving the service running in the background. The default is "true". BaseDirectory (string) If set, instructs the filter to change to the specified directory using chdir(2) before doing anything else. This means any files referenced elsewhere in the configuration file can be specified rel- ative to this directory. It's also useful for arranging that any crash dumps will be saved to a specific location. BodyLengthDB (dataset) Requests that opendkim include a "l=" body length tag when the set contains any of the envelope recipient addresses. The addresses presented are tested against the database in various forms as de- scribed under the SigningTable setting (below). This feature of the protocol exists to improve the likelihood that a signature will sur- vive transit through a mailing list server, as they commonly append footers to messages. Note, however, that this creates a potential security issue since someone could add arbitrary text to the signed message and the signature would still validate. See the DKIM speci- fication for details. BogusKey (string) Instructs the filter to treat a passing signature associated with a bogus (forged) key in a special way. Possible values are neutral (return a "neutral" result), none (take no special action) and fail (return a "fail" result; this is the default). CaptureUnknownErrors (Boolean) When set, and on systems where MTA quarantine is available, the fil- ter will request quarantine of a message that results in an internal error or resource exhaustion. Canonicalization (string) Selects the canonicalization method(s) to be used when signing mes- sages. When verifying, the message's DKIM-Signature: header field specifies the canonicalization method. The recognized values are relaxed and simple as defined by the DKIM specification. The de- fault is simple. The value may include two different canonicaliza- tions separated by a slash ("/") character, in which case the first will be applied to the header and the second to the body. ChangeRootDirectory (string) Requests that the operating system change the effective root direc- tory of the process to the one specified here prior to beginning ex- ecution. chroot(2) requires superuser access. A warning will be generated if UserID is not also set. CheckSigningTable (Boolean) If set to yes, it walks the SigningTable when loading the config file to check for missing keys in KeyTable. The default is yes. ClockDrift (integer) Sets the tolerance in seconds to be applied when determining whether a signature was either expired or generated in the future. The de- fault is 300. Diagnostics (Boolean) Requests the inclusion of "z=" tags in signatures, which encode the original header field set for use by verifiers when diagnosing veri- fication failures. Not recommended for normal operation. DiagnosticDirectory (string) Directory into which to write diagnostic reports when message veri- fication fails on a message bearing a "z=" tag. If not set (the de- fault), these files are not generated. DisableCryptoInit (Boolean) If set, skips initialization of the SSL library initialization steps, which are normally required in multi-threaded environments. This assumes some other library opendkim is using will do the re- quired initialization and shutdown. DNSConnect (Boolean) Requests that the asynchronous resolver start using TCP immediately rather than using UDP until TCP is actually needed. Does not work with all resolvers. DNSTimeout (integer) Sets the DNS timeout in seconds. A value of 0 causes an infinite wait. The default is 5. Ignored if not using an asynchronous re- solver package. See also the NOTES section below. Domain (dataset) A set of domains whose mail should be signed by this filter. Mail from other domains will be verified rather than being signed. This parameter is not required if a SigningTable is in use; in that case, the list of signed domains is implied by the lines in that file. This parameter is ignored if a KeyTable is defined. DomainKeysCompat (boolean) If set, backward compatibility with DomainKeys (RFC4870) key records is enabled. When not set, such keys are considered to be syntacti- cally invalid. DontSignMailTo (dataset) A set of e-mail address, mail to which should never be signed by the filter. Note that this is an "any" feature; if any one of the re- cipients of the message matches a member of this list, the message will not be signed. EnableCoredumps (boolean) On systems that have such support, make an explicit request to the kernel to dump cores when the filter crashes for some reason. Some modern UNIX systems suppress core dumps during crashes for security reasons if the user ID has changed during the lifetime of the process. Currently only supported on Linux. ExemptDomains (dataset) Specifies a set of domains, mail from which should be ignored en- tirely by the filter. This is similar to the PeerList setting ex- cept that it bases its decision on the sender of the message as identified from the header fields or other message data, not the identity of the SMTP client sending the message. ExternalIgnoreList (dataset) Identifies a set of "external" hosts that may send mail through the server as one of the signing domains without credentials as such. This has the effect of suppressing the "external host (hostname) tried to send mail as (domain)" log messages. Entries in the data set should be of the same form as those of the PeerList option be- low. The set is empty by default. FinalPolicyScript (string) Gives the name of a Lua script that should be run after the entire message has been received. This can be used to enact local policy decisions such as message rejection, quarantine, rerouting, etc. based on signatures found on the message, the results of attempts to verify them, and other properties of the message or signatures. See opendkim-lua(3) for details. FixCRLF (Boolean) Requests that the DKIM library convert bare CRs and LFs to CRLFs during body canonicalization, anticipating that an MTA somewhere be- fore delivery will do that conversion anyway. The default is to leave them as-is. IdentityHeader (string) This specifies the header field where an identity is stored. (Ex- perimental feature not enabled for this installation.) IdentityHeaderRemove (Boolean) Remove the IdentityHeader after signing. (Experimental feature not enabled for this installation.) IgnoreMalformedMail (boolean) Silently passes malformed messages without alteration. This in- cludes messages that fail the RequiredHeaders check, if enabled. The default is to pass those messages but add an Authentication-Re- sults field indicating that they were malformed. Include (string) Names a file to be opened and read as an additional configuration file. Nesting is allowed to a maximum of five levels. InternalHosts (dataset) Identifies a set internal hosts whose mail should be signed rather than verified. Entries in this data set follow the same form as those of the PeerList option below. If not specified, the default of "127.0.0.1" is applied. Naturally, providing a value here over- rides the default, so if mail from 127.0.0.1 should be signed, the list provided here should include that address explicitly. KeepAuthResults (boolean) Suppresses removal of Authentication-Results header fields contain- ing DKIM results apparently added by this filter (usually the result of a misconfiguration or a forgery). KeepTemporaryFiles (boolean) Instructs the filter to create temporary files containing the header and body canonicalizations of messages that are signed or verified. The location of these files can be set using the TemporaryDirectory parameter. Intended only for debugging verification problems. KeyFile (string) Gives the location of a PEM-formatted private key to be used for signing all messages. Ignored if a KeyTable is defined. If the key is an Ed25519 key, SignatureAlgorithm is automatically set to ed25519-sha256. An explicit SignatureAlgorithm setting is not re- quired. KeyTable (dataset) Gives the location of a file mapping key names to signing keys. If present, overrides any KeyFile setting in the configuration file. The data set named here maps each key name to three values: (a) the name of the domain to use in the signature's "d=" value; (b) the name of the selector to use in the signature's "s=" value; and (c) either a private key or a path to a file containing a private key; (d) (optional) signing algorithm to use with this key. If the first value consists solely of a percent sign ("%") character, it will be replaced by the apparent domain of the sender when generating a sig- nature. If the third value starts with a slash ("/") character, or "./" or "../", then it is presumed to refer to a file from which the private key should be read, otherwise it is itself a PEM-encoded private key or a base64-encoded DER private key; a "%" in the third value in this case will be replaced by the apparent domain name of the sender. The fourth field should be one of supported signing al- gorithms (see SignatureAlgorithm below). If it is omitted, the al- gorithm specified in SignatureAlgorithm is used for the key. Sign- ingTable (see below) is used to select records from this table to be used to add signatures based on the message sender. To sign each message with both RSA and Ed25519, create two KeyTable entries (one per algorithm) and two SigningTable rules that both match the sending domain, then enable MultipleSignatures. For exam- ple: # KeyTable (file or inline dataset) rsa-key %:rsa2024:/etc/opendkim/keys/%.rsa.private:rsa-sha256 ed-key %:ed2024:/etc/opendkim/keys/%.ed25519.private:ed25519-sha256 # SigningTable *@example.com rsa-key *@example.com ed-key # opendkim.conf MultipleSignatures yes Note that the motivation for dual-algorithm signing is as a contin- gency against a future cryptographic weakness in one algorithm; no such weakness in RSA has been discovered at the time of this writ- ing. While Ed25519 produces smaller DNS records and shorter keys than RSA, the savings in the context of modern mail headers are trivial. Signing with multiple algorithms requires each validating server to verify all signatures, increasing load on both sides, and provides no immediate security benefit in normal operation. Opera- tors should have a clear reason before enabling this feature; it is most useful for interoperability testing. When a message is verified by a server running this software, it will produce a single Authentication-Results header containing one dkim= entry per signature, for example: Authentication-Results: example.com; dkim=pass header.d=example.com header.s=rsa2024 header.a=rsa-sha256; dkim=fail header.d=example.com header.s=ed2024 header.a=ed25519-sha256 RFC 6376 requires that each signature be evaluated independently but does not define what a verifier or downstream tool should conclude when results are mixed. This is left to local policy. OpenDKIM treats a message as passing if any signature passes; a stricter im- plementation may treat any dkim=fail entry as a failure regardless of other results. Downstream tools that inspect Authentication-Re- sults headers, including but not limited to SpamAssassin, may behave differently and in ways that are not easily predicted. Operators should test the full mail path before deploying multi-algorithm signing in production. LDAPAuthMechanism (string) Names the authentication mechanism to use when connecting to an LDAP server. The default is the empty string, meaning "simple" authenti- cation should be done. LDAPAuthName (string) Specifies the authenticating name to use when using SASL to authen- ticate to an LDAP server. Requires SASL support be installed on the local system. There is no default. LDAPAuthRealm (string) Specifies the authentication realm to use when using SASL to authen- ticate to an LDAP server. Requires SASL support be installed on the local system. There is no default. LDAPAuthUser (string) Specifies the authenticating user to use when using SASL to authen- ticate to an LDAP server. Requires SASL support be installed on the local system. There is no default. LDAPBindPassword (string) Specifies the password to use when conducting an LDAP "bind" opera- tion. There is no default. LDAPBindUser (string) Specifies the user ID to use when conducting an LDAP "bind" opera- tion. There is no default. LDAPDisableCache (Boolean) Suppresses creation of a local cache in front of LDAP queries. LDAPKeepaliveIdle (integer) Sets the number of seconds a connection to an LDAP server needs to remain idle before TCP starts sending keepalive probes. If not specified, the LDAP library default is used. LDAPKeepaliveInterval (integer) Sets the interval in seconds between TCP keepalive probes. If not specified, the LDAP library default is used. LDAPKeepaliveProbes (integer) Sets the maximum number of keepalive probes TCP should send before abandoning the connection. If not specified, the LDAP library de- fault is used. LDAPTimeout (integer) Sets the time in seconds after which an LDAP operation should be abandoned. The default is 5. LDAPUseTLS (Boolean) Indicates whether or not a TLS connection should be established when contacting an LDAP server. The default is "False". LogResults (boolean) If logging is enabled (see Syslog and StdoutLog below), requests that the results of evaluation of all signatures that were at least partly intact (i.e., the "d=", "s=", and "b=" tags could be ex- tracted). LogWhy (boolean) If logging is enabled (see Syslog and StdoutLog below), issues very detailed logging about the logic behind the filter's decision to ei- ther sign a message or verify it. The logic behind the decision is non-trivial and can be confusing to administrators not familiar with its operation. A description of how the decision is made can be found in the OPERATIONS section of the opendkim(8) man page. This causes a large increase in the amount of log data generated for each message, so it should be limited to debugging use and not enabled for general operation. MacroList (dataset) Defines a set of MTA-provided macros that 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 speci- fied matching a macro name in the data set, 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, meaning macros are not considered when making the sign-verify decision. The general format of the value is 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. In order for the macro and its value to be available to the filter for checking, the MTA must send it during the protocol exchange. This is either accomplished via manual configuration of the MTA to send the desired macros or, for MTA/filter combinations that support the feature, the filter can request those macros that are of inter- est. The latter is a feature negotiated at the time the filter re- ceives a connection from the MTA and its availability depends upon the version of milter used to compile the filter and the version of the MTA making the connection. This data set must be of type "file" or "csl". MaximumHeaders (integer) Defines the maximum number of bytes the header block of a message may consume before the filter will reject the message. This miti- gates a denial-of-service attack in which a client connects to the MTA and begins feeding an unbounded number of header fields of arbi- trary 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. MaximumSignaturesToVerify (integer) Defines the maximum number of signatures on a message for which ver- ification should be conducted. The default is three. Signatures are selected from the top of the message downward. If TrustSigna- turesFrom is set, signatures from domains in that data set are al- ways verified, which may consume part or all of, or even exceed, this limit. 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 implies use of BodyLengthDB for all addresses. MilterDebug (integer) Sets the debug level to be requested from the milter library. Cur- rently, the highest meaningful value is 6. Minimum (string) Instructs the verification code to fail messages for which a partial signature was received. There are three possible formats: min indi- cating at least min bytes of the message must be signed (or if the message is smaller than min then all of it must be signed); min% re- quiring that at least min percent of the received message must be signed; and min+ meaning there may be no more than min bytes of un- signed data appended to the message for it to be considered valid. MinimumKeyBits (integer) Establishes a minimum key size for acceptable signatures. Signa- tures with smaller key sizes, even if they otherwise pass DKIM vali- dation, will me marked as invalid. The default is 1024. A value of 0 accepts all keys. Mode (string) Selects operating modes. The string is a concatenation of charac- ters that indicate which mode(s) of operation are desired. Valid modes are s (signer) and v (verifier). The default is sv except in test mode (see the opendkim(8) man page) in which case the default is v. When signing mode is enabled, one of the following combina- tions must also be set: (a) Domain, KeyFile, Selector, no KeyTable, no SigningTable; (b) KeyTable, SigningTable, no Domain, no KeyFile, no Selector; (c) KeyTable, SetupPolicyScript, no Domain, no KeyFile, no Selector. MTA (dataset) A set of MTA names (a la the sendmail(8) DaemonPortOptions Name pa- rameter) whose mail should be signed by this filter. There is no default, meaning MTA name is not considered when making the sign- verify decision. MTACommand (string) Specifies the path to an executable to be used for sending mail such as that generated by SendReports. The default is /usr/sbin/send- mail. The executable should accept typical sendmail(8) command line options "-t" (take addresses from message body) and "-f" (set enve- lope sender), accept the new message on its standard input, and re- turn a non-zero exit status on any error. MultipleSignatures (Boolean) Allow addition of multiple signatures when a signing table is in use. See SigningTable for more information. MustBeSigned (dataset) Specifies a set of header fields that, if present, must be covered by the DKIM signature when verifying a message. If a header field in this set is present in the message and is not signed, the filter will treat even an otherwise valid signature as invalid. The de- fault is an empty list. Nameservers (string) Provides a comma-separated list of IP addresses that are to be used when doing DNS queries to retrieve DKIM keys, VBR records, etc. These override any local defaults built in to the resolver in use, which may be defined in /etc/resolv.conf or hard-coded into the software. NoHeaderB (Boolean) If set, this feature suppresses the use of "header.b" tags in added Authentication-Results header fields. The default is "false", which means those tags will be applied. OmitHeaders (dataset) Specifies a set of header fields that should be omitted when gener- ating signatures. If an entry in the list names any header field that is mandated by the DKIM specification, the entry is ignored. A set of header fields is listed in the DKIM specification (RFC6376, Section 5.4) as "SHOULD NOT" be signed; the default list for this parameter contains those fields (Return-Path, Received, Comments, Keywords, Bcc, Resent-Bcc and DKIM-Signature). To omit no headers, simply use the string "." (or any string that will match no header field names). Specifying a list with this parameter replaces the default entirely, unless one entry is "*", which stands for the de- fault set itself and causes the remaining entries to be interpreted as a delta to that default; for example, "*,+foobar" will use the entire default list plus the name "foobar", while "*,-Bcc" would use the entire default list except for the "Bcc" entry. Note that none of the headers in the default OmitHeaders list appear in the default SignHeaders list either. This setting acts as a safety override: it prevents headers from being signed even if they are explicitly added to SignHeaders. On-BadSignature (string) Selects the action to be taken when a signature fails to validate. Possible values (with abbreviated forms in parentheses): accept (a) accept the message; discard (d) discard the message; quarantine (q) quarantine the message; reject (r) reject the message; tempfail (t) temp-fail the message. The default is accept. Note that the "t" (testing) flag in a DKIM key bypasses this behaviour; a bad signa- ture that references a testing flag will still be delivered, though the added Authentication-Results field will indicate both the failed result and the test mode so that consumers of the message can take appropriate action. On-Default (string) Selects the action to be taken when any verification or internal er- ror of any kind is encountered. This is processed before the other "On-" values so it can be used as a blanket setting followed by spe- cific overrides. Possible values are the same as those for On- BadSignature. Use with caution in production: setting this to accept will cause the fil- ter to pass messages through regardless of any verification error condi- tion. It is most useful during initial deployment or troubleshooting, com- bined with specific On- overrides for conditions you want to enforce. On-DNSError (string) Selects the action to be taken when a transient DNS error is encoun- tered. Possible values are the same as those for On-BadSignature. The default is tempfail. 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 On- BadSignature. The default is tempfail. On-KeyNotFound (string) Selects the action to be taken when the key referenced by a signa- ture is not present in the DNS. Possible values are the same as those for On-BadSignature. The default is accept. On-NoSignature (string) Selects the action to be taken when a message arrives unsigned. Possible values are the same as those for On-BadSignature. The de- fault is accept. 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 On-BadSignature. The default is tempfail. On-SignatureError (string) Selects the action to be taken when a message cannot be signed be- cause of issues with the message or the key provided for signing. Possible values are the same as those for On-BadSignature. The de- fault is reject. OversignHeaders (dataset) Specifies a set of header fields that should be included in all sig- nature header lists (the "h=" tag) once more than the number of times they were actually present in the signed message. The set is empty by default. The purpose of this, and especially of listing an absent header field, is to prevent the addition of important fields between the signer and the verifier. Since the verifier would in- clude that header field when performing verification if it had been added by an intermediary, the signed message and the verified mes- sage were different and the verification would fail. Listing a header field name once more than it appears is sufficient to block any number of later additions; it is not necessary to list it more times than that. Note that this technique is useful even for header fields that RFC5322 permits only once (such as From), since not all mail-handling software enforces RFC5322 header field count restric- tions. Oversigning From is strongly recommended and is the default. A message with multiple From headers is non-compliant (RFC5322, Section 3.6 requires exactly one), but an attacker who controls an intermediate MTA can exploit the inconsistency: prepend a malicious From header, let DKIM verify the original one, and rely on the receiving MUA displaying the injected header rather than the signed one. Oversigning From prevents this by causing ver- ification to fail whenever a second From header is present. See also RFC6376 Section 8.15 and RFC5322 Section 3.6. The oversigning mechanism works by appending each listed field name an ex- tra time to the signature's h= tag. For this to provide any protection, the field must also be present in the set of headers actually being signed (via SignHeaders or the compiled-in default set). If a field name appears here but not in the signing set, it will appear only once in h= as a phan- tom empty-header entry. The resulting signature is technically valid, but the oversigning protection is silently absent: a verifier will accept a message that has had that header injected downstream. Any field listed here must therefore also appear in SignHeaders (or be covered by the * de- fault expansion). See RFC6376, Section 5.4 for further discussion. Unlike SignHeaders and OmitHeaders, this parameter does not support the *,+,- delta syntax, as there is no default set to expand. PeerList (dataset) Identifies a set of "peers" that identifies clients whose connec- tions should be accepted without processing by this filter. The set should contain on each line a hostname, domain name (e.g. ".exam- ple.com"), IP address, an IPv6 address (including an IPv4 mapped ad- dress), 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. Host and domain names are matched first, then the IP or IPv6 address depending on the connection type. More precise entries are preferred over less precise ones, i.e. "192.168.1.1" will match be- fore "!192.168.1.0/24". The text form of IPv6 addresses will be forced to lowercase when queried (RFC5952), so the contents of this data set should also use lowercase. CIDR notation must use 0 for all unmasked bits (e.g. "10.0.0.1/8" will never match). IPv6 addresses, whether single or in CIDR notation, must appear in the form produced by inet_ntop(3) which replaces consecutive zeros with "::" (e.g. "0:0:0:0:0:0:0:1" will never match). The IP address portion of an entry may option- ally contain square brackets; both forms (with and without) will be checked. Note: IPv6 addresses cannot be specified inline in opendkim.conf be- cause the colons in an IPv6 address (e.g. "fd00:368::/40") are in- distinguishable from the "type:" prefix used to identify dataset types (e.g. "file:", "ldap:"). IPv6 entries must be placed in a separate file and referenced with the file: prefix, for example: PeerList file:/etc/opendkim/peerlist.txt where peerlist.txt contains one entry per line, including any IPv6 addresses or CIDR ranges. PidFile (string) Specifies the path to a file that should be created at process start containing the process ID. POPDBFile (dataset) Requests that the filter consult a set for IP addresses that should be allowed for signing. This feature was designed for POP-before- SMTP datastores. (Not enabled for this installation.) Quarantine (Boolean) Requests that messages which fail verification be quarantined by the MTA. (Requires a sufficiently recent version of the milter li- brary.) QueryCache (Boolean) Instructs the DKIM library to maintain its own local cache of keys and policies retrieved from DNS, rather than relying on the name- server for caching service. Useful if the nameserver being used by the filter is not local. (Not enabled for this installation.) RedirectFailuresTo (address) Messages bearing signatures that failed to verify are redirected to the specified address. The original envelope recipient set is recorded in the header before redirection occurs. By default, no redirection is done. RemoveARAll (Boolean) Removes all Authentication-Results: header fields that also satisfy the requirements of RemoveARFrom below. By default, only those con- taining a DKIM result are removed. RemoveARFrom (dataset) Defines a set of hostnames whose Authentication-Results: header fields should be removed before the message is passed for delivery. By default only those header fields matching the local host's canon- ical name will be removed. Matching is only done on full hostnames (e.g. "host.example.com") or on domain names (e.g. ".example.com"). RemoveOldSignatures (Boolean) Removes all existing signatures when operating in signing mode. ReplaceHeaders (data set) Defines a set of header fields that should be affected by the text replacement rules defined by the ReplaceRules setting. By default, all header fields are included. (Experimental feature not enabled for this installation.) ReplaceRules (string) Specifies a file containing a list of text replacement rules that are applied to the message header fields to replace certain content expected to be changed as the message passes through local MTAs. This can be used to accommodate expected changes such as those made to From: fields by MTA "masquerade" features. Each entry in the file consists of a POSIX regular expression, followed by a tab (ASCII 9), followed by the text that should be used to replace the text matching the expression. The '#' character denotes the begin- ning of a comment and text from that point on in a single line is ignored. Blank lines are also skipped. (Experimental feature not enabled for this installation.) ReportAddress (string) Specifies the string to use in the From: header field for outgoing reports (see SendReports below). If not specified, the executing user and local hostname will be used to construct the address. ReportBccAddress (string) Specifies address(es) to include in a Bcc: header field on outgoing reports (see SendReports below). If multiple addresses are required, they should be comma separated. RequestReports (boolean) When signing, includes a request for signature evaluation failures in the signature. (See RFC6651 for details.) RequiredHeaders (boolean) Checks all messages for compliance with RFC5322 header field count requirements. Non-compliant messages are rejected. RequireSafeKeys (boolean) When reading a key file, a message will be logged if the key file has the read or write bit set other than for the owner or for a group that the executing process is in. With this feature set to "true", the filter will further consider this an error and refuse to make use of the file's contents. The default is "true". ResignAll (boolean) Where ResignMailTo triggers a re-signing action, this flag indicates whether or not all mail should be signed (if set) versus only veri- fied mail being signed (if not set). (Experimental feature not en- abled for this installation.) ResignMailTo (dataset) Checks each message recipient against the specified dataset for a matching record. The full address is checked in each case, then the hostname, then each domain preceded by ".". If there is a match, the value returned is presumed to be the name of a key in the KeyTable (if defined) to be used to re-sign the message in addition to verifying it. If there is a match without a KeyTable, the de- fault key is applied. (Experimental feature not enabled for this installation.) ResolverConfiguration (string) Provides the given string as configuration information to the under- lying resolver. For the standard UNIX resolver, this is unused; for Unbound, the string contains a filename that is considered to be a configuration file. There is no default. ResolverTracing (Boolean) Requests resolver tracing features be enabled, if available. The effect of this depends on how debugging features of the resolver might be implemented. Currently only effective with the OpenDKIM asynchronous resolver library. ScreenPolicyScript (string) Gives the name of a Lua script that should be run after all of the header fields have been processed for a message; in particular, this is useful after all DKIM signatures have been detected and initial evaluation has been done. The script has access to all of the header fields and connection information and can direct that certain signatures be ignored based on that information. See opendkim- lua(3) for details. SelectCanonicalizationHeader (string) Defines a header field name which, if present, adjusts which canoni- calization will be used to generate an outgoing signature. Over- rides the Canonicalization setting if the header field is present. The default is "X-Canonicalization". Selector (string) Defines the name of the selector to be used when signing messages. See the DKIM specification for details. Used only when signing with a single key; see the SigningTable parameter below for more informa- tion. This parameter is ignored if a KeyTable is defined. SenderHeaders (dataset) Specifies an ordered list of header fields that should be searched to determine the sender of a message. The first header field found is the one whose value is used. This is mainly used when signing for deciding which signing request(s) to make. By default, the "From" header field is the only one checked. See the OmitHeaders setting for a description of possible values. SenderMacro (string) Use the milter macro string to determine the sender of the message. (Experimental feature not enabled for this installation.) SendReports (Boolean) If true, when a signature verification fails and the signature in- cluded a reporting request ("r=y") and the signing domain advertises a reporting address (i.e. ra=user) in a reporting record in the DNS, the filter will send a structured report to that address con- taining details needed to reproduce the problem. See RFC6651 for a complete description of this mechanism. SetupPolicyScript (string) Gives the name of a Lua script that should be run once all header fields for a message have arrived. The script has access to all of the header fields and connection information and can request DKIM verification or signing based on that information. See opendkim- lua(3) for details. SignatureAlgorithm (string) Selects the signing algorithm to use when generating signatures. Use 'opendkim -V' to see the list of supported algorithms. The de- fault is rsa-sha256 if it is available, otherwise it will be rsa- sha1. This setting must match the type of key specified by KeyFile or the key's entry in KeyTable. In particular, Ed25519 keys require this to be set to ed25519-sha256 explicitly, as the algorithm is not auto-detected from the key type. 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. SignHeaders (dataset) Specifies the comma-separated set of header fields that should be included when generating signatures. If the list omits any header field that is mandated by the DKIM specification, those fields are implicitly added. A set of header fields is listed in the DKIM specification as "Common examples" to be signed (RFC6376, Section 5.4.1); the base default list for this parameter contains those fields (From, Reply-To, Subject, Date, To, Cc, Resent-Date, Resent- From, Resent-Sender, Resent-To, Resent-Cc, In-Reply-To, References, List-Id, List-Help, List-Unsubscribe, List-Subscribe, List-Post, List-Owner, List-Archive). Specifying a list with this parameter replaces the default entirely, unless one entry is "*", which stands for the default set itself and causes the remaining entries to be interpreted as a delta to that default; for example, "*,+foobar" will use the entire default list plus the name "foobar", while "*,-Bcc" would use the entire default list except for the "Bcc" en- try. The RFC 6376 default set does not include MIME structure headers. The rec- ommended configuration extends the default with Content-Type, MIME-Version, and Content-Transfer-Encoding (using the *,+header delta syntax). Leaving these headers unsigned allows an attacker with the ability to modify a mes- sage in transit to alter the MIME structure without invalidating the DKIM signature: for example, changing Content-Type from text/plain to text/html causes the same body to render entirely differently, or wrapping the body in a multipart container allows new content to be injected after the signed portion. See also the OversignHeaders setting and RFC6376 Section 8.15. If you specify an explicit header list without *, be careful not to omit any field that is also listed in OversignHeaders. Doing so removes it from the signing set, which silently disables the oversigning protection for that field: the signature will still verify, but a downstream injected copy of that header will no longer cause verification to fail. Using the * delta syntax is the safest way to extend the default set without inadver- tently dropping fields required by other settings. SigningTable (dataset) Defines a table used to select one or more signatures to apply to a message based on the address found in the From: header field. Keys in this table vary depending on the type of table used; values in this data set should include one field that contains a name found in the KeyTable (see above) that identifies which key should be used in generating the signature, and an optional second field naming the signer of the message that will be included in the "i=" tag in the generated signature. Note that the "i=" value will not be included in the signature if it conflicts with the signing domain (the "d=" value). If the first field contains only a "%" character, it will be re- placed by the domain found in the From: header field. Similarly, within the optional second field, any "%" character will be replaced by the domain found in the From: header field. If this table specifies a regular expression file ("refile"), then the keys are wildcard patterns that are matched against the address found in the From: header field. Entries are checked in the order in which they appear in the file. For all other database types, the full user@host is checked first, then simply host, then user@.domain (with all superdomains checked in sequence, so "foo.example.com" would first check "user@foo.exam- ple.com", then "user@.example.com", then "user@.com"), then .domain, then user@*, and finally *. In any case, only the first match is applied, unless MultipleSigna- tures is enabled in which case all matches are applied. SMTPURI (string) Specifies a URI (e.g., "smtp://localhost") to which mail should be sent via SMTP when notifications are generated. (Not enabled for this installation.) Socket (string) Specifies the socket that should be established by the filter to re- ceive 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] or inet6:port[@host] which creates a TCP socket on the specified port and in the specified protocol family. If the host is not given as either a hostname or an IP address, the socket will be listening on all interfaces. A literal IP address must be enclosed in square brackets. This option is mandatory either in the configuration file or on the command line. SoftStart (Boolean) If set, the inability to connect and authenticate to an LDAP or SQL server will not prevent the filter from starting, and reconnections will be attempted for each query. The default is "False". SoftwareHeader (Boolean) Causes opendkim to add an "DKIM-Filter" header field 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 field's contents. Note that the header field is not added if the Mode setting causes the message to be ignored (e.g., if only signing mode is enabled and the configuration causes the mes- sage not to be signed, or only verify mode is enabled and configura- tion would otherwise have caused the message to be signed, then it will not have this header field added). Statistics (filename) This specifies a file in which to store DKIM transaction statistics. See opendkim-stats(8) for a mechanism to parse the file's contents, and opendkim-importstats() for a mechanism to translate the file's contents into SQL database insertions. (Experimental feature not enabled for this installation.) StatisticsName (string) Defines the name to be used as the reporting host in statistics logs. By default, the local host's name returned by gethostname(3) is used. (Experimental feature not enabled for this installation.) StatisticsPolicyScript (string) The statistics script is run after all of the DKIM verification and signing work has been completed but before any final message han- dling is done. The main purpose of this script is to give the user an opportunity to examine the message or its signatures and make ar- bitrary additional statistical observations that should be recorded by the statistics module. StatisticsPrefix (string) When AnonymousStatistics is enabled, this string may be specified and will be prepended to all data before hashing for more complete anonymization. This means two records from different sources refer- encing the same source will still produce different hashes, meaning such correlation is now only possible within the data from a single repoter. StrictHeaders (Boolean) If set, instructs the DKIM library to refuse processing of a message if the header field count does not conform to RFC5322 Section 3.6. StrictTestMode (Boolean) Selects strict CRLF mode during testing (see the -t command line flag in the opendkim(8) man page); messages for which all header fields and body lines are not CRLF-terminated are considered mal- formed and will produce an error. SubDomains (Boolean) Sign subdomains of those listed by the Domain parameter as well as the actual domains. Syslog (Boolean) Log via calls to syslog(3) any interesting activity. SyslogFacility (string) Log via calls to syslog(3) using the named facility. The facility names are the same as the ones allowed in syslog.conf(5). The de- fault is "mail". SyslogName (string) Log via calls to syslog(3) using that name. That way one could dis- tinguish multiple instances. The default is the name of the exe- cutable, normally "opendkim". SyslogSuccess (Boolean) Log via calls to syslog(3) additional entries indicating successful signing or verification of messages. StdoutLog (Boolean) Log any interesting activity to standard output. The SyslogSuccess parameter has the same affect with this parameter as it has with the Syslog parameter. TemporaryDirectory (string) Specifies the directory in which temporary canonicalization files should be written. The default is to use the libopendkim default location, currently /tmp. TestDNSData (data set) Provides a data set whose keys will be treated as DNS record names and values as TXT record contents. Intended for use during auto- mated testing. TestPublicKeys (string) Names a file from which public keys should be read. Intended for use only during automated testing. TrustAnchorFile (string) Specifies a file from which trust anchor data should be read when doing DNS queries and applying the DNSSEC protocol. This is cur- rently ignored unless the underlying library is compiled to use Un- bound; see the documentation at at http://unbound.net for the ex- pected format of this file. TrustSignaturesFrom (dataset) This value consists of a set of domains that are considered trust- worthy in terms of third-party signatures. That is, if a message arrives with a signature from a domain that doesn't match the domain in the From: header, this setting determines whether or not that signature will be trusted. If this value is undefined, all signa- tures are trusted. UMask (integer) Requests a specific permissions mask to be used for file creation. This only really applies to creation of the socket when Socket spec- ifies a UNIX domain socket, and to the PidFile (if any); temporary files are created by the mkstemp(3) function that enforces a spe- cific file mode on creation regardless of the process umask. See umask(2) for more information. UnprotectedKey (string) Instructs the filter to treat a passing signature associated with a key found in an insecure (i.e. not protected by DNSSEC) DNS record in a special way. Possible values are neutral (return a "neutral" result), none (take no special action; this is the default) and fail (return a "fail" result). UserID (string) Attempts to become the specified userid before starting operations. The value is of the form userid[:group]. The process will be as- signed all of the groups and primary group ID of the named userid unless an alternate group is specified. VBR-Certifiers (string) The default certifiers if not specified in X-VBR-Certifiers header field. (Experimental feature not enabled for this installation.) VBR-PurgeFields (string) If set, arranges to remove X-VBR-Certifiers and X-VBR-Type fields on messages prior to sending them. (Experimental feature not enabled for this installation.) VBR-TrustedCertifiers (string) A colon or comma sparated list of trusted certifiers to accept when verifying VBR-Info header field. (Experimental feature not enabled for this installation.) VBR-TrustedCertifiersOnly (Boolean) By default, the certifiers that are in both the trusted certifiers list (above) and those in the message's VBR-Info header field will be checked for vouching. With this option set, the trusted certi- fiers will be checked and the ones claimed by the message will be ignored. (Experimental feature not enabled for this installation.) VBR-Type (string) This default VBR type if not specified in the X-VBR-Type header field. (Experimental feature not enabled for this installation.) WeakSyntaxChecks (Boolean) Requests that the library continue processing messages even if syn- tax errors are discovered early in message analysis. This means, for example, that a signed message with a mangled From: field will still proceed to verification even if the author's domain could not be determined. NOTES When using DNS timeouts (see the DNSTimeout 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. Features that involve specification of IPv4 addresses or CIDR blocks will use the inet_addr(3) function to parse that information. Users should be familiar with the way that function handles the non-trivial cases (for ex- ample, "192.0.2/24" and "192.0.2.0/24" are not the same thing). FILES /usr/local/etc/opendkim.conf Default location of this file. VERSION This man page covers version 2.11.0 of opendkim. COPYRIGHT Copyright (c) 2007, 2008, Sendmail, Inc. and its suppliers. All rights re- served. Copyright (c) 2009-2015, The Trusted Domain Project. All rights reserved. SEE ALSO opendkim(8), opendkim-lua(3), sendmail(8) RFC5451 - Message Header Field for Indicating Message Authentication Status RFC5617 - DKIM Author Domain Signing Practises RFC5965 - An Extensible Format for Email Feedback Reports RFC6008 - Authentication-Results Registration for Differentiating among Cryptographic Results RFC6376 - DomainKeys Identified Mail RFC6651 - Extensions to DomainKeys Identified Mail (DKIM) for Failure Re- porting The Trusted Domain Project opendkim.conf(5)
NAME | LOCATION | DESCRIPTION | PARAMETERS | NOTES | FILES | VERSION | COPYRIGHT | SEE ALSO
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