X-Git-Url: https://git.exim.org/users/jgh/exim.git/blobdiff_plain/9973c745f74341d8ffddabac4b05ade9be2f4310..05e4f4dea8e993a6ad0f4e6cba092226155bc6e1:/doc/doc-docbook/spec.xfpt diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index dc924678d..bca6689b6 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -45,14 +45,14 @@ . Update the Copyright year (only) when changing content. . ///////////////////////////////////////////////////////////////////////////// -.set previousversion "4.91" +.set previousversion "4.92" .include ./local_params .set ACL "access control lists (ACLs)" .set I "    " .macro copyyear -2018 +2018, 2019 .endmacro . ///////////////////////////////////////////////////////////////////////////// @@ -371,13 +371,11 @@ contributors. .section "Exim documentation" "SECID1" . Keep this example change bar when updating the documentation! -.new .cindex "documentation" This edition of the Exim specification applies to version &version() of Exim. Substantive changes from the &previousversion; edition are marked in some renditions of this document; this paragraph is so marked if the rendition is capable of showing a change indicator. -.wen This document is very much a reference manual; it is not a tutorial. The reader is expected to have some familiarity with the SMTP mail transfer protocol and @@ -1888,11 +1886,10 @@ to your &_Local/Makefile_& and rebuild Exim. .section "Including TLS/SSL encryption support" "SECTinctlsssl" .cindex "TLS" "including support for TLS" .cindex "encryption" "including support for" -.cindex "SUPPORT_TLS" .cindex "OpenSSL" "building Exim with" .cindex "GnuTLS" "building Exim with" -Exim can be built to support encrypted SMTP connections, using the STARTTLS -command as per RFC 2487. It can also support legacy clients that expect to +Exim is usually built to support encrypted SMTP connections, using the STARTTLS +command as per RFC 2487. It can also support clients that expect to start a TLS session immediately on connection to a non-standard port (see the &%tls_on_connect_ports%& runtime option and the &%-tls-on-connect%& command line option). @@ -1901,35 +1898,41 @@ If you want to build Exim with TLS support, you must first install either the OpenSSL or GnuTLS library. There is no cryptographic code in Exim itself for implementing SSL. +.new +If you do not want TLS support you should set +.code +DISABLE_TLS=yes +.endd +in &_Local/Makefile_&. +.wen + If OpenSSL is installed, you should set .code -SUPPORT_TLS=yes +USE_OPENSL=yes TLS_LIBS=-lssl -lcrypto .endd in &_Local/Makefile_&. You may also need to specify the locations of the OpenSSL library and include files. For example: .code -SUPPORT_TLS=yes +USE_OPENSL=yes TLS_LIBS=-L/usr/local/openssl/lib -lssl -lcrypto TLS_INCLUDE=-I/usr/local/openssl/include/ .endd .cindex "pkg-config" "OpenSSL" If you have &'pkg-config'& available, then instead you can just use: .code -SUPPORT_TLS=yes +USE_OPENSL=yes USE_OPENSSL_PC=openssl .endd .cindex "USE_GNUTLS" If GnuTLS is installed, you should set .code -SUPPORT_TLS=yes USE_GNUTLS=yes TLS_LIBS=-lgnutls -ltasn1 -lgcrypt .endd in &_Local/Makefile_&, and again you may need to specify the locations of the library and include files. For example: .code -SUPPORT_TLS=yes USE_GNUTLS=yes TLS_LIBS=-L/usr/gnu/lib -lgnutls -ltasn1 -lgcrypt TLS_INCLUDE=-I/usr/gnu/include @@ -1937,7 +1940,6 @@ TLS_INCLUDE=-I/usr/gnu/include .cindex "pkg-config" "GnuTLS" If you have &'pkg-config'& available, then instead you can just use: .code -SUPPORT_TLS=yes USE_GNUTLS=yes USE_GNUTLS_PC=gnutls .endd @@ -2530,6 +2532,8 @@ use of Exim's filtering capabilities, you should make the document entitled If you are already running Exim on your host, building and installing a new version automatically makes it available to MUAs, or any other programs that call the MTA directly. However, if you are running an Exim daemon, you do need +.cindex restart "on HUP signal" +.cindex signal "HUP, to restart" to send it a HUP signal, to make it re-execute itself, and thereby pick up the new binary. You do not need to stop processing mail in order to install a new version of Exim. The install script does not modify an existing runtime @@ -2628,6 +2632,7 @@ supplementary group is one of those listed in the &%trusted_groups%& configuration option. Note that the Exim group is not automatically trusted. .cindex '&"From"& line' +.cindex "envelope from" .cindex "envelope sender" Trusted users are always permitted to use the &%-f%& option or a leading &"From&~"& line to specify the envelope sender of a message that is passed to @@ -2767,7 +2772,12 @@ used to specify a path on the command line if a pid file is required. The SIGHUP signal .cindex "SIGHUP" +.cindex restart "on HUP signal" +.cindex signal "HUP, to restart" .cindex "daemon" "restarting" +.cindex signal "to reload configuration" +.cindex daemon "reload configuration" +.cindex reload configuration can be used to cause the daemon to re-execute itself. This should be done whenever Exim's configuration file, or any file that is incorporated into it by means of the &%.include%& facility, is changed, and also whenever a new version @@ -2877,6 +2887,7 @@ separate document entitled &'Exim's interfaces to mail filtering'&. When testing a filter file, .cindex "&""From""& line" +.cindex "envelope from" .cindex "envelope sender" .oindex "&%-f%&" "for filter testing" the envelope sender can be set by the &%-f%& option, @@ -3661,14 +3672,12 @@ The &`timestamp`& selector causes the current time to be inserted at the start of all debug output lines. This can be useful when trying to track down delays in processing. -.new .cindex debugging "UTF-8 in" .cindex UTF-8 "in debug output" The &`noutf8`& selector disables the use of UTF-8 line-drawing characters to group related information. When disabled. ascii-art is used instead. Using the &`+all`& option does not set this modifier, -.wen If the &%debug_print%& option is set in any driver, it produces output whenever any debugging is selected, or if &%-v%& is used. @@ -3719,6 +3728,7 @@ between &%-F%& and the <&'string'&> is optional. .cindex "sender" "address" .cindex "address" "sender" .cindex "trusted users" +.cindex "envelope from" .cindex "envelope sender" .cindex "user" "trusted" This option sets the address of the envelope sender of a locally-generated @@ -3953,6 +3963,20 @@ is sent to the sender, containing the text &"cancelled by administrator"&. Bounce messages are just discarded. This option can be used only by an admin user. +.new +.vitem &%-MG%&&~<&'queue&~name'&&~<&'message&~id'&>&~<&'message&~id'&>&~... +.oindex "&%-MG%&" +.cindex queue named +.cindex "named queues" +.cindex "queue" "moving messages" +This option requests that each listed message be moved from its current +queue to the given named queue. +The destination queue name argument is required, but can be an empty +string to define the default queue. +If the messages are not currently located in the default queue, +a &%-qG%& option will be required to define the source queue. +.wen + .vitem &%-Mmad%&&~<&'message&~id'&>&~<&'message&~id'&>&~... .oindex "&%-Mmad%&" .cindex "delivery" "cancelling all" @@ -6253,18 +6277,22 @@ Two remote transports and four local transports are defined. remote_smtp: driver = smtp message_size_limit = ${if > {$max_received_linelength}{998} {1}{0}} -.ifdef _HAVE_DANE - dnssec_request_domains = * - hosts_try_dane = * +.ifdef _HAVE_PRDR + hosts_try_prdr = * .endif .endd This transport is used for delivering messages over SMTP connections. The list of remote hosts comes from the router. The &%message_size_limit%& usage is a hack to avoid sending on messages with over-long lines. The built-in macro _HAVE_DANE guards configuration -to try to use DNSSEC for all queries and to use DANE for delivery; +to use DANE for delivery; see section &<>& for more details. +The &%hosts_try_prdr%& option enables an efficiency SMTP option. It is +negotiated between client and server and not expected to cause problems +but can be disabled if needed. The built-in macro _HAVE_PRDR guards the +use of the &%hosts_try_prdr%& configuration option. + The other remote transport is used when delivering to a specific smarthost with whom there must be some kind of existing relationship, instead of the usual federated system. @@ -6299,6 +6327,9 @@ smarthost_smtp: tls_require_ciphers = SECURE192:-VERS-SSL3.0:-VERS-TLS1.0:-VERS-TLS1.1 .endif .endif +.ifdef _HAVE_PRDR + hosts_try_prdr = * +.endif .endd After the same &%message_size_limit%& hack, we then specify that this Transport can handle messages to multiple domains in one run. The assumption here is @@ -6318,6 +6349,9 @@ ROUTER_SMARTHOST macro, because that is unaffected by CNAMEs present in DNS. You want to specify the hostname which you'll expect to validate for, and that should not be subject to insecure tampering via DNS results. +For the &%hosts_try_prdr%& option see the previous transport. + +All other options are defaulted. .code local_delivery: driver = appendfile @@ -6643,11 +6677,10 @@ aliases or other indexed data referenced by an MTA. Information about cdb and tools for building the files can be found in several places: .display &url(https://cr.yp.to/cdb.html) -&url(http://www.corpit.ru/mjt/tinycdb.html) +&url(https://www.corpit.ru/mjt/tinycdb.html) &url(https://packages.debian.org/stable/utils/freecdb) &url(https://github.com/philpennock/cdbtools) (in Go) .endd -. --- 2018-09-07: corpit.ru http:-only A cdb distribution is not needed in order to build Exim with cdb support, because the code for reading cdb files is included directly in Exim itself. However, no means of building or testing cdb files is provided with Exim, so @@ -6731,6 +6764,31 @@ lookup types support only literal keys. &*Warning 2*&: In a host list, you must always use &(net-iplsearch)& so that the implicit key is the host's IP address rather than its name (see section &<>&). + +.new +&*Warning 3*&: Do not use an IPv4-mapped IPv6 address for a key; use the +IPv4, in dotted-quad form. (Exim converts IPv4-mapped IPv6 addresses to this +notation before executing the lookup.) +.wen +.next +.new +.cindex lookup json +.cindex json "lookup type" +.cindex JSON expansions +&(json)&: The given file is a text file with a JSON structure. +An element of the structure is extracted, defined by the search key. +The key is a list of subelement selectors +(colon-separated by default but changeable in the usual way) +which are applied in turn to select smaller and smaller portions +of the JSON structure. +If a selector is numeric, it must apply to a JSON array; the (zero-based) +nunbered array element is selected. +Otherwise it must apply to a JSON object; the named element is selected. +The final resulting element can be a simple JSON type or a JSON object +or array; for the latter two a string-representation os the JSON +is returned. +For elements of type string, the returned value is de-quoted. +.wen .next .cindex "linear search" .cindex "lookup" "lsearch" @@ -7284,7 +7342,7 @@ with the lookup. With &"strict"& a response from the DNS resolver that is not labelled as authenticated data is treated as equivalent to a temporary DNS error. -The default is &"never"&. +The default is &"lax"&. See also the &$lookup_dnssec_authenticated$& variable. @@ -8649,8 +8707,12 @@ to quote keys was made available in &(lsearch)& files. However, the more recently implemented &(iplsearch)& files do require colons in IPv6 keys (notated using the quoting facility) so as to distinguish them from IPv4 keys. For this reason, when the lookup type is &(iplsearch)&, IPv6 addresses are -converted using colons and not dots. In all cases, full, unabbreviated IPv6 +converted using colons and not dots. +.new +In all cases except IPv4-mapped IPv6, full, unabbreviated IPv6 addresses are always used. +The latter are converted to IPv4 addresses, in dotted-quad form. +.wen Ideally, it would be nice to tidy up this anomalous situation by changing to colons in all cases, given that quoting is now available for &(lsearch)&. @@ -9159,6 +9221,7 @@ Many strings in Exim's runtime configuration are expanded before use. Some of them are expanded every time they are used; others are expanded only once. When a string is being expanded it is copied verbatim from left to right except +.cindex expansion "string concatenation" when a dollar or backslash character is encountered. A dollar specifies the start of a portion of the string that is interpreted and replaced as described below in section &<>& onwards. Backslash is used as an @@ -9169,7 +9232,13 @@ dependent upon the option for which a value is sought; in this documentation, options for which string expansion is performed are marked with † after the data type. ACL rules always expand strings. A couple of expansion conditions do not expand some of the brace-delimited branches, for security -reasons. +reasons, +.new +.cindex "tainted data" expansion +.cindex expansion "tainted data" +and expansion of data deriving from the sender (&"tainted data"&) +is not permitted. +.wen @@ -9319,7 +9388,7 @@ If the ACL returns defer the result is a forced-fail. Otherwise the expansion f .cindex headers "authentication-results:" .cindex authentication "expansion item" This item returns a string suitable for insertion as an -&'Authentication-Results"'& +&'Authentication-Results:'& header line. The given <&'authserv-id'&> is included in the result; typically this will be a domain name identifying the system performing the authentications. @@ -9507,8 +9576,9 @@ ${extract{Z}{A=... B=...}{$value} fail } This forces an expansion failure (see section &<>&); {<&'string2'&>} must be present for &"fail"& to be recognized. -.new .vitem "&*${extract json{*&<&'key'&>&*}{*&<&'string1'&>&*}{*&<&'string2'&>&*}&&& + {*&<&'string3'&>&*}}*&" &&& + "&*${extract jsons{*&<&'key'&>&*}{*&<&'string1'&>&*}{*&<&'string2'&>&*}&&& {*&<&'string3'&>&*}}*&" .cindex "expansion" "extracting from JSON object" .cindex JSON expansions @@ -9523,10 +9593,16 @@ The expanded <&'string1'&> must be of the form: The braces, commas and colons, and the quoting of the member name are required; the spaces are optional. Matching of the key against the member names is done case-sensitively. +For the &"json"& variant, +if a returned value is a JSON string, it retains its leading and +trailing quotes. +.new +For the &"jsons"& variant, which is intended for use with JSON strings, the +leading and trailing quotes are removed from the returned value. +.wen . XXX should be a UTF-8 compare The results of matching are handled as above. -.wen .vitem "&*${extract{*&<&'number'&>&*}{*&<&'separators'&>&*}&&& @@ -9560,8 +9636,9 @@ yields &"99"&. Two successive separators mean that the field between them is empty (for example, the fifth field above). -.new -.vitem "&*${extract json{*&<&'number'&>&*}}&&& +.vitem "&*${extract json {*&<&'number'&>&*}}&&& + {*&<&'string1'&>&*}{*&<&'string2'&>&*}{*&<&'string3'&>&*}}*&" &&& + "&*${extract jsons{*&<&'number'&>&*}}&&& {*&<&'string1'&>&*}{*&<&'string2'&>&*}{*&<&'string3'&>&*}}*&" .cindex "expansion" "extracting from JSON array" .cindex JSON expansions @@ -9570,6 +9647,12 @@ apart from leading and trailing white space, which is ignored. Field selection and result handling is as above; there is no choice of field separator. +For the &"json"& variant, +if a returned value is a JSON string, it retains its leading and +trailing quotes. +.new +For the &"jsons"& variant, which is intended for use with JSON strings, the +leading and trailing quotes are removed from the returned value. .wen @@ -9589,7 +9672,7 @@ input, but a separator setting is not included in the output. For example: ${filter{a:b:c}{!eq{$item}{b}}} .endd yields &`a:c`&. At the end of the expansion, the value of &$item$& is restored -to what it was before. See also the &*map*& and &*reduce*& expansion items. +to what it was before. See also the &%map%& and &%reduce%& expansion items. .vitem &*${hash{*&<&'string1'&>&*}{*&<&'string2'&>&*}{*&<&'string3'&>&*}}*& @@ -9940,8 +10023,8 @@ setting is not included in the output. For example: ${map{a:b:c}{[$item]}} ${map{<- x-y-z}{($item)}} .endd expands to &`[a]:[b]:[c] (x)-(y)-(z)`&. At the end of the expansion, the -value of &$item$& is restored to what it was before. See also the &*filter*& -and &*reduce*& expansion items. +value of &$item$& is restored to what it was before. See also the &%filter%& +and &%reduce%& expansion items. .vitem &*${nhash{*&<&'string1'&>&*}{*&<&'string2'&>&*}{*&<&'string3'&>&*}}*& .cindex "expansion" "numeric hash" @@ -10083,14 +10166,12 @@ Example, to not do so (preferred, eg. by some webservers): .code ${readsocket{/socket/name}{request string}{3s:shutdown=no}} .endd -.new The second, tls, controls the use of TLS on the connection. Example: .code ${readsocket{/socket/name}{request string}{3s:tls=yes}} .endd The default is to not use TLS. If it is enabled, a shutdown as descripbed above is never done. -.wen A fourth argument allows you to change any newlines that are in the data that is read, in the same way as for &%readfile%& (see above). This example @@ -10142,7 +10223,7 @@ assigned to the &$value$& variable. After this, each item in the <&'string1'&> list is assigned to &$item$&, in turn, and <&'string3'&> is expanded for each of them. The result of that expansion is assigned to &$value$& before the next iteration. When the end of the list is reached, the final value of &$value$& is -added to the expansion output. The &*reduce*& expansion item can be used in a +added to the expansion output. The &%reduce%& expansion item can be used in a number of ways. For example, to add up a list of numbers: .code ${reduce {<, 1,2,3}{0}{${eval:$value+$item}}} @@ -10153,7 +10234,7 @@ can be found: ${reduce {3:0:9:4:6}{0}{${if >{$item}{$value}{$item}{$value}}}} .endd At the end of a &*reduce*& expansion, the values of &$item$& and &$value$& are -restored to what they were before. See also the &*filter*& and &*map*& +restored to what they were before. See also the &%filter%& and &%map%& expansion items. .vitem &*$rheader_*&<&'header&~name'&>&*:*&&~or&~&*$rh_*&<&'header&~name'&>&*:*& @@ -10413,9 +10494,9 @@ separator explicitly: ${addresses:>:$h_from:} .endd -Compare the &*address*& (singular) +Compare the &%address%& (singular) expansion item, which extracts the working address from a single RFC2822 -address. See the &*filter*&, &*map*&, and &*reduce*& items for ways of +address. See the &%filter%&, &%map%&, and &%reduce%& items for ways of processing lists. To clarify "list of addresses in RFC 2822 format" mentioned above, Exim follows @@ -10903,11 +10984,15 @@ If the string is a single variable of type certificate, returns the SHA-1 hash fingerprint of the certificate. -.vitem &*${sha256:*&<&'string'&>&*}*& +.vitem &*${sha256:*&<&'string'&>&*}*& &&& + &*${sha2:*&<&'string'&>&*}*& &&& + &*${sha2_:*&<&'string'&>&*}*& .cindex "SHA-256 hash" +.cindex "SHA-2 hash" .cindex certificate fingerprint .cindex "expansion" "SHA-256 hashing" .cindex "&%sha256%& expansion item" +.cindex "&%sha2%& expansion item" The &%sha256%& operator computes the SHA-256 hash value of the string and returns it as a 64-digit hexadecimal number, in which any letters are in upper case. @@ -10915,6 +11000,15 @@ it as a 64-digit hexadecimal number, in which any letters are in upper case. If the string is a single variable of type certificate, returns the SHA-256 hash fingerprint of the certificate. +.new +The operator can also be spelled &%sha2%& and does the same as &%sha256%& +(except for certificates, which are not supported). +Finally, if an underbar +and a number is appended it specifies the output length, selecting a +member of the SHA-2 family of hash functions. +Values of 256, 384 and 512 are accepted, with 256 being the default. +.wen + .vitem &*${sha3:*&<&'string'&>&*}*& &&& &*${sha3_:*&<&'string'&>&*}*& @@ -11012,7 +11106,6 @@ Case is defined per the system C locale. .cindex "expansion" "utf-8 forcing" .cindex "&%utf8clean%& expansion item" This replaces any invalid utf-8 sequence in the string by the character &`?`&. -.new In versions of Exim before 4.92, this did not correctly do so for a truncated final codepoint's encoding, and the character would be silently dropped. If you must handle detection of this scenario across both sets of Exim behavior, @@ -11025,7 +11118,6 @@ condition = ${if inlist{${utf8clean:${length_1:$local_part}}}{:?}{yes}{no}} .endd (which will false-positive if the first character of the local part is a literal question mark). -.wen .vitem "&*${utf8_domain_to_alabel:*&<&'string'&>&*}*&" &&& "&*${utf8_domain_from_alabel:*&<&'string'&>&*}*&" &&& @@ -11297,11 +11389,30 @@ list separator is changed to a comma: .code ${if forany{<, $recipients}{match{$item}{^user3@}}{yes}{no}} .endd -The value of &$item$& is saved and restored while &*forany*& or &*forall*& is +The value of &$item$& is saved and restored while &%forany%& or &%forall%& is being processed, to enable these expansion items to be nested. To scan a named list, expand it with the &*listnamed*& operator. +.new +.vitem "&*forall_json{*&<&'a JSON array'&>&*}{*&<&'a condition'&>&*}*&" &&& + "&*forany_json{*&<&'a JSON array'&>&*}{*&<&'a condition'&>&*}*&" &&& + "&*forall_jsons{*&<&'a JSON array'&>&*}{*&<&'a condition'&>&*}*&" &&& + "&*forany_jsons{*&<&'a JSON array'&>&*}{*&<&'a condition'&>&*}*&" +.cindex JSON "iterative conditions" +.cindex JSON expansions +.cindex expansion "&*forall_json*& condition" +.cindex expansion "&*forany_json*& condition" +.cindex expansion "&*forall_jsons*& condition" +.cindex expansion "&*forany_jsons*& condition" +As for the above, except that the first argument must, after expansion, +be a JSON array. +The array separator is not changeable. +For the &"jsons"& variants the elements are expected to be JSON strings +and have their quotes removed before the evaluation of the condition. +.wen + + .vitem &*ge&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& &&& &*gei&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& @@ -11979,6 +12090,15 @@ contain the trailing slash. If &$config_file$& does not contain a slash, .vindex "&$config_file$&" The name of the main configuration file Exim is using. +.new +.vitem &$dmarc_domain_policy$& &&& + &$dmarc_status$& &&& + &$dmarc_status_text$& &&& + &$dmarc_used_domains$& +Results of DMARC verification. +For details see section &<>&. +.wen + .vitem &$dkim_verify_status$& Results of DKIM verification. For details see section &<>&. @@ -12112,6 +12232,7 @@ This variable contains the version string of the Exim build. The first character is a major version number, currently 4. Then after a dot, the next group of digits is a minor version number. There may be other characters following the minor version. +This value may be overridden by the &%exim_version%& main config option. .vitem &$header_$&<&'name'&> This is not strictly an expansion variable. It is expansion syntax for @@ -12205,7 +12326,7 @@ the result, the name is not accepted, and &$host_lookup_deferred$& is set to .cindex authentication "expansion item" Performing these checks sets up information used by the -&$authresults$& expansion item. +&%authresults%& expansion item. .vitem &$host_lookup_failed$& @@ -12671,6 +12792,16 @@ or if not set, the value of &$qualify_domain$&. .cindex queues named The name of the spool queue in use; empty for the default queue. +.new +.vitem &$r_...$& +.vindex &$r_...$& +.cindex router variables +Values can be placed in these variables by the &%set%& option of a router. +They can be given any name that starts with &$r_$&. +The values persist for the address being handled through subsequent routers +and the eventual transport. +.wen + .vitem &$rcpt_count$& .vindex "&$rcpt_count$&" When a message is being received by SMTP, this variable contains the number of @@ -13233,6 +13364,9 @@ or a &%def%& condition. &*Note*&: Under versions of OpenSSL preceding 1.1.1, when a list of more than one file is used for &%tls_certificate%&, this variable is not reliable. +.new +The macro "_TLS_BAD_MULTICERT_IN_OURCERT" will be defined for those versions. +.wen .vitem &$tls_in_peercert$& .vindex "&$tls_in_peercert$&" @@ -13289,6 +13423,12 @@ The deprecated &$tls_cipher$& variable is the same as &$tls_in_cipher$& during m but in the context of an outward SMTP delivery taking place via the &(smtp)& transport becomes the same as &$tls_out_cipher$&. +.new +.vitem &$tls_in_cipher_std$& +.vindex "&$tls_in_cipher_std$&" +As above, but returning the RFC standard name for the cipher suite. +.wen + .vitem &$tls_out_cipher$& .vindex "&$tls_out_cipher$&" This variable is @@ -13297,6 +13437,12 @@ and then set to the outgoing cipher suite if one is negotiated. See chapter &<>& for details of TLS support and chapter &<>& for details of the &(smtp)& transport. +,new +.vitem &$tls_out_cipher_std$& +.vindex "&$tls_out_cipher_std$&" +As above, but returning the RFC standard name for the cipher suite. +.wen + .vitem &$tls_out_dane$& .vindex &$tls_out_dane$& DANE active status. See section &<>&. @@ -13431,7 +13577,8 @@ Otherwise, empty. .vitem &$version_number$& .vindex "&$version_number$&" -The version number of Exim. +The version number of Exim. Same as &$exim_version$&, may be overridden +by the &%exim_version%& main config option. .vitem &$warn_message_delay$& .vindex "&$warn_message_delay$&" @@ -14225,7 +14372,9 @@ listed in more than one group. See also the &'Policy controls'& section above. .table2 -.row &%dkim_verify_signers%& "DKIM domain for which DKIM ACL is run" +.row &%dkim_verify_hashes%& "DKIM hash methods accepted for signatures" +.row &%dkim_verify_keytypes%& "DKIM key types accepted for signatures" +.row &%dkim_verify_signers%& "DKIM domains for which DKIM ACL is run" .row &%host_lookup%& "host name looked up for these hosts" .row &%host_lookup_order%& "order of DNS and local name lookups" .row &%recipient_unqualified_hosts%& "may send unqualified recipients" @@ -14270,6 +14419,7 @@ See also the &'Policy controls'& section above. .row &%ignore_fromline_hosts%& "allow &""From ""& from these hosts" .row &%ignore_fromline_local%& "allow &""From ""& from local SMTP" .row &%pipelining_advertise_hosts%& "advertise pipelining to these hosts" +.row &%pipelining_connect_advertise_hosts%& "advertise pipelining to these hosts" .row &%prdr_enable%& "advertise PRDR to all hosts" .row &%smtputf8_advertise_hosts%& "advertise SMTPUTF8 to these hosts" .row &%tls_advertise_hosts%& "advertise TLS to these hosts" @@ -14555,13 +14705,20 @@ recommended, except when you have no other choice. .cindex "UTF-8" "in domain name" Lots of discussion is going on about internationalized domain names. One camp is strongly in favour of just using UTF-8 characters, and it seems -that at least two other MTAs permit this. This option allows Exim users to -experiment if they wish. +that at least two other MTAs permit this. +This option allows Exim users to experiment if they wish. If it is set true, Exim's domain parsing function allows valid UTF-8 multicharacters to appear in domain name components, in addition to -letters, digits, and hyphens. However, just setting this option is not -enough; if you want to look up these domain names in the DNS, you must also +letters, digits, and hyphens. + +.new +If Exim is built with internationalization support +and the SMTPUTF8 ESMTP option is in use (see chapter &<>&) +this option can be left as default. +.wen +Without that, +if you want to look up such domain names in the DNS, you must also adjust the value of &%dns_check_names_pattern%& to match the extended form. A suitable setting is: .code @@ -14969,6 +15126,27 @@ etc. are ignored. If IP literals are enabled, the &(ipliteral)& router declines to handle IPv6 literal addresses. +.new +.option dkim_verify_hashes main "string list" "sha256 : sha512 : sha1" +.cindex DKIM "selecting signature algorithms" +This option gives a list of hash types which are acceptable in signatures, +and an order of processing. +Signatures with algorithms not in the list will be ignored. + +Note that the presence of sha1 violates RFC 8301. +Signatures using the rsa-sha1 are however (as of writing) still common. +The default inclusion of sha1 may be dropped in a future release. + +.option dkim_verify_keytypes main "string list" "ed25519 : rsa" +This option gives a list of key types which are acceptable in signatures, +and an order of processing. +Signatures with algorithms not in the list will be ignored. + +.option dkim_verify_minimal main boolean false +If set to true, verification of signatures will terminate after the +first success. +.wen + .option dkim_verify_signers main "domain list&!!" $dkim_signers .cindex DKIM "controlling calls to the ACL" This option gives a list of DKIM domains for which the DKIM ACL is run. @@ -15026,7 +15204,6 @@ This option controls whether or not an IP address, given as a CSA domain, is reversed and looked up in the reverse DNS, as described in more detail in section &<>&. -.new .option dns_cname_loops main integer 1 .cindex DNS "CNAME following" This option controls the following of CNAME chains, needed if the resolver does @@ -15037,7 +15214,6 @@ If you have an ancient one, a value of 10 is likely needed. The default value of one CNAME-follow is needed thanks to the observed return for an MX request, given no MX presence but a CNAME to an A, of the CNAME. -.wen .option dns_dnssec_ok main integer -1 @@ -15062,6 +15238,11 @@ domain matches this list. This is a fudge to help with name servers that give big delays or otherwise do not work for the AAAA record type. In due course, when the world's name servers have all been upgraded, there should be no need for this option. +.new +Note that all lookups, including those done for verification, are affected; +this will result in verify failure for IPv6 connections or ones using names +only valid for IPv6 addresses. +.wen .option dns_retrans main time 0s @@ -15264,6 +15445,14 @@ not also supplied, the gid is taken from the result of &[getpwnam()]& if it is used. See chapter &<>& for a discussion of security issues. +.option exim_version main string "current version" +.cindex "Exim version" +.cindex customizing "version number" +.cindex "version number of Exim" override +This option allows to override the &$version_number$&/&$exim_version$& Exim reports in +various places. Use with care, this may fool stupid security scanners. + + .option extra_local_interfaces main "string list" unset This option defines network interfaces that are to be considered local when routing, but which are not used for listening by the daemon. See section @@ -15783,6 +15972,7 @@ and no &'Sender:'& header is ever added. If, in addition, you want to retain &'Sender:'& header lines supplied by untrusted users, you must also set &%local_sender_retain%& to be true. +.cindex "envelope from" .cindex "envelope sender" These options affect only the header lines in the message. The envelope sender is still forced to be the login id at the qualify domain unless @@ -15883,6 +16073,10 @@ when Exim is entered, so it can, for example, contain a reference to the host name. If no specific path is set for the log files at compile or runtime, or if the option is unset at runtime (i.e. &`log_file_path = `&) they are written in a sub-directory called &_log_& in Exim's spool directory. +.new +A path must start with a slash. +To send to syslog, use the word &"syslog"&. +.wen Chapter &<>& contains further details about Exim's logging, and section &<>& describes how the contents of &%log_file_path%& are used. If this string is fixed at your installation (contains no expansion @@ -16089,7 +16283,7 @@ harm. This option overrides the &%pipe_as_creator%& option of the &(pipe)& transport driver. -.option openssl_options main "string list" "+no_sslv2 +single_dh_use +no_ticket" +.option openssl_options main "string list" "+no_sslv2 +no_sslv3 +single_dh_use +no_ticket" .cindex "OpenSSL "compatibility options" This option allows an administrator to adjust the SSL options applied by OpenSSL to connections. It is given as a space-separated list of items, @@ -16269,6 +16463,21 @@ for each SMTP command and response. When PIPELINING is advertised, Exim assumes that clients will use it; &"out of order"& commands that are &"expected"& do not count as protocol errors (see &%smtp_max_synprot_errors%&). +.new +.option pipelining_connect_advertise_hosts main "host list&!!" * +.cindex "pipelining" "early connection" +.cindex "pipelining" PIPE_CONNECT +If Exim is built with the SUPPORT_PIPE_CONNECT build option +this option controls which hosts the facility is advertised to +and from which pipeline early-connection (before MAIL) SMTP +commands are acceptable. +When used, the pipelining saves on roundtrip times. + +See also the &%hosts_pipe_connect%& smtp transport option. + +Currently the option name &"X_PIPE_CONNECT"& is used. +.wen + .option prdr_enable main boolean false .cindex "PRDR" "enabling on server" @@ -16529,23 +16738,26 @@ on at the end (preceded by a semicolon). The string is expanded each time it is used. If the expansion yields an empty string, no &'Received:'& header line is added to the message. Otherwise, the string should start with the text &"Received:"& and conform to the RFC 2822 specification for &'Received:'& -header lines. The default setting is: +header lines. +.new +The default setting is: .code received_header_text = Received: \ ${if def:sender_rcvhost {from $sender_rcvhost\n\t}\ - {${if def:sender_ident \ - {from ${quote_local_part:$sender_ident} }}\ - ${if def:sender_helo_name {(helo=$sender_helo_name)\n\t}}}}\ + {${if def:sender_ident \ + {from ${quote_local_part:$sender_ident} }}\ + ${if def:sender_helo_name {(helo=$sender_helo_name)\n\t}}}}\ by $primary_hostname \ - ${if def:received_protocol {with $received_protocol}} \ - ${if def:tls_in_cipher {($tls_in_cipher)\n\t}}\ + ${if def:received_protocol {with $received_protocol }}\ + ${if def:tls_in_cipher_std { tls $tls_in_cipher_std\n\t}}\ (Exim $version_number)\n\t\ ${if def:sender_address \ {(envelope-from <$sender_address>)\n\t}}\ id $message_exim_id\ ${if def:received_for {\n\tfor $received_for}} .endd +.wen The reference to the TLS cipher is omitted when Exim is built without TLS support. The use of conditional expansions ensures that this works for both @@ -16724,11 +16936,11 @@ it qualifies them only if the message came from a host that matches &%sender_unqualified_hosts%&, or if the message was submitted locally (not using TCP/IP), and the &%-bnq%& option was not set. -.option set_environment main "string list" empty +.option add_environment main "string list" empty .cindex "environment" -This option allows to set individual environment variables that the +This option allows to add individual environment variables that the currently linked libraries and programs in child processes use. The -default list is empty, +default list is empty. .option slow_lookup_log main integer 0 @@ -17470,8 +17682,8 @@ is not required the &%tls_advertise_hosts%& option should be set empty. .cindex "TLS" "server certificate; location of" .cindex "certificate" "server, location of" The value of this option is expanded, and must then be a list of absolute paths to -files which contains the server's certificates. Commonly only one file is -needed. +files which contain the server's certificates (in PEM format). +Commonly only one file is needed. The server's private key is also assumed to be in this file if &%tls_privatekey%& is unset. See chapter &<>& for further details. @@ -17482,14 +17694,14 @@ use when sending messages as a client, you must set the &%tls_certificate%& option in the relevant &(smtp)& transport. &*Note*&: If you use filenames based on IP addresses, change the list -separator in the usual way (&<>&) >to avoid confusion under IPv6. +separator in the usual way (&<>&) to avoid confusion under IPv6. &*Note*&: Under versions of OpenSSL preceding 1.1.1, when a list of more than one file is used, the &$tls_in_ourcert$& variable is unreliable. - -&*Note*&: OCSP stapling is not usable under OpenSSL -when a list of more than one file is used. +.new +The macro "_TLS_BAD_MULTICERT_IN_OURCERT" will be defined for those versions. +.wen If the option contains &$tls_out_sni$& and Exim is built against OpenSSL, then if the OpenSSL build supports TLS extensions and the TLS client sends the @@ -17540,7 +17752,14 @@ larger prime than requested. The value of this option is expanded and indicates the source of DH parameters to be used by Exim. -&*Note: The Exim Maintainers strongly recommend using a filename with site-generated +.new +This option is ignored for GnuTLS version 3.6.0 and later. +The library manages parameter negotiation internally. +.wen + +&*Note: The Exim Maintainers strongly recommend, +for other TLS library versions, +using a filename with site-generated local DH parameters*&, which has been supported across all versions of Exim. The other specific constants available are a fallback so that even when "unconfigured", Exim can offer Perfect Forward Secrecy in older ciphersuites in TLS. @@ -17635,11 +17854,37 @@ status proof for the server's certificate, as obtained from the Certificate Authority. Usable for GnuTLS 3.4.4 or 3.3.17 or OpenSSL 1.1.0 (or later). +.new +The macro "_HAVE_TLS_OCSP" will be defined for those versions. +.wen -For GnuTLS 3.5.6 or later the expanded value of this option can be a list +.new +For OpenSSL 1.1.0 or later, and +.wen +for GnuTLS 3.5.6 or later the expanded value of this option can be a list of files, to match a list given for the &%tls_certificate%& option. The ordering of the two lists must match. +.new +The macro "_HAVE_TLS_OCSP_LIST" will be defined for those versions. +.wen +.new +The file(s) should be in DER format, +except for GnuTLS 3.6.3 or later +or for OpenSSL, +when an optional filetype prefix can be used. +The prefix must be one of "DER" or "PEM", followed by +a single space. If one is used it sets the format for subsequent +files in the list; the initial format is DER. +If multiple proofs are wanted, for multiple chain elements +(this only works under TLS1.3) +they must be coded as a combined OCSP response. + +Although GnuTLS will accept PEM files with multiple separate +PEM blobs (ie. separate OCSP responses), it sends them in the +TLS Certificate record interleaved with the certificates of the chain; +although a GnuTLS client is happy with that, an OpenSSL client is not. +.wen .option tls_on_connect_ports main "string list" unset .cindex SSMTP @@ -17797,6 +18042,7 @@ See &%unknown_login%&. .cindex "sender" "setting by untrusted user" .cindex "untrusted user setting sender" .cindex "user" "untrusted setting sender" +.cindex "envelope from" .cindex "envelope sender" When an untrusted user submits a message to Exim using the standard input, Exim normally creates an envelope sender address from the user's login and the @@ -17947,6 +18193,10 @@ file = ${extract{mailbox}{$address_data}} This makes the configuration file less messy, and also reduces the number of lookups (though Exim does cache lookups). +.new +See also the &%set%& option below. +.wen + .vindex "&$sender_address_data$&" .vindex "&$address_data$&" The &%address_data%& facility is also useful as a means of passing information @@ -18152,7 +18402,7 @@ or for any deliveries caused by this router. You should not set this option unless you really, really know what you are doing. See also the generic transport option of the same name. -.option dnssec_request_domains routers "domain list&!!" unset +.option dnssec_request_domains routers "domain list&!!" * .cindex "MX record" "security" .cindex "DNSSEC" "MX lookup" .cindex "security" "MX lookup" @@ -18199,6 +18449,7 @@ Not effective on redirect routers. .option errors_to routers string&!! unset +.cindex "envelope from" .cindex "envelope sender" .cindex "router" "changing address for errors" If a router successfully handles an address, it may assign the address to a @@ -18727,11 +18978,24 @@ latter kind. This option controls whether the local part is used to form the key for retry hints for addresses that suffer temporary errors while being handled by this -router. The default value is true for any router that has &%check_local_user%& +.new +router. The default value is true for any router that has any of +&%check_local_user%&, +&%local_parts%&, +&%condition%&, +&%local_part_prefix%&, +&%local_part_suffix%&, +&%senders%& or +&%require_files%& +.wen set, and false otherwise. Note that this option does not apply to hints keys for transport delays; they are controlled by a generic transport option of the same name. +Failing to set this option when it is needed +(because a remote router handles only some of the local-parts for a domain) +can result in incorrect error messages being generated. + The setting of &%retry_use_local_part%& applies only to the router on which it appears. If the router generates child addresses, they are routed independently; this setting does not become attached to them. @@ -18860,6 +19124,32 @@ SMTP VRFY command is enabled, it must be used after MAIL if the sender address matters. +.new +.option set routers "string list" unset +.cindex router variables +This option may be used multiple times on a router; +because of this the list aspect is mostly irrelevant. +The list separator is a semicolon but can be changed in the +usual way. + +Each list-element given must be of the form $"name = value"$ +and the names used must start with the string &"r_"&. +Values containing a list-separator should have them doubled. +When a router runs, the strings are evaluated in order, +to create variables which are added to the set associated with +the address. +The variable is set with the expansion of the value. +The variables can be used by the router options +(not including any preconditions) +and by the transport. +Later definitions of a given named variable will override former ones. +Varible use is via the usual &$r_...$& syntax. + +This is similar to the &%address_data%& option, except that +many independent variables can be used, with choice of naming. +.wen + + .option translate_ip_address routers string&!! unset .cindex "IP address" "translating" .cindex "packet radio" @@ -21645,6 +21935,7 @@ on a remote transport in the current implementation. .option return_path transports string&!! unset .cindex "envelope sender" +.cindex "envelope from" .cindex "transport" "return path; changing" .cindex "return path" "changing in transport" If this option is set, the string is expanded at transport time and replaces @@ -22639,6 +22930,15 @@ sometimes add other information onto the ends of message filenames. Section &<>& contains further information. +.new +This option should not be used when other message-handling software +may duplicate messages by making hardlinks to the files. When that is done Exim +will count the message size once for each filename, in contrast with the actual +disk usage. When the option is not set, calculating total usage requires +a system-call per file to get the size; the number of links is then available also +as is used to adjust the effective size. +.wen + .option quota_warn_message appendfile string&!! "see below" See below for the use of this option. If it is not set when @@ -22691,6 +22991,7 @@ percentage. .option use_bsmtp appendfile boolean false +.cindex "envelope from" .cindex "envelope sender" If this option is set true, &(appendfile)& writes messages in &"batch SMTP"& format, with the envelope sender and recipient(s) included as SMTP commands. If @@ -23567,14 +23868,15 @@ command = /bin/sh -c ${lookup{$local_part}lsearch{/some/file}} .cindex "filter" "transport filter" .vindex "&$pipe_addresses$&" Special handling takes place when an argument consists of precisely the text -&`$pipe_addresses`&. This is not a general expansion variable; the only +&`$pipe_addresses`& (no quotes). +This is not a general expansion variable; the only place this string is recognized is when it appears as an argument for a pipe or transport filter command. It causes each address that is being handled to be inserted in the argument list at that point &'as a separate argument'&. This avoids any problems with spaces or shell metacharacters, and is of use when a &(pipe)& transport is handling groups of addresses in a batch. -If &%force_command%& is enabled on the transport, Special handling takes place +If &%force_command%& is enabled on the transport, special handling takes place for an argument that consists of precisely the text &`$address_pipe`&. It is handled similarly to &$pipe_addresses$& above. It is expanded and each argument is inserted in the argument list at that point @@ -24231,15 +24533,23 @@ of the message. Its value must not be zero. See also &%final_timeout%&. .option dkim_canon smtp string&!! unset +DKIM signing option. For details see section &<>&. .option dkim_domain smtp string list&!! unset +DKIM signing option. For details see section &<>&. .option dkim_hash smtp string&!! sha256 +DKIM signing option. For details see section &<>&. .option dkim_identity smtp string&!! unset +DKIM signing option. For details see section &<>&. .option dkim_private_key smtp string&!! unset +DKIM signing option. For details see section &<>&. .option dkim_selector smtp string&!! unset +DKIM signing option. For details see section &<>&. .option dkim_strict smtp string&!! unset +DKIM signing option. For details see section &<>&. .option dkim_sign_headers smtp string&!! "per RFC" +DKIM signing option. For details see section &<>&. .option dkim_timestamps smtp string&!! unset -DKIM signing options. For details see section &<>&. +DKIM signing option. For details see section &<>&. .option delay_after_cutoff smtp boolean true @@ -24281,14 +24591,15 @@ See the &%search_parents%& option in chapter &<>& for more details. -.option dnssec_request_domains smtp "domain list&!!" unset +.option dnssec_request_domains smtp "domain list&!!" * .cindex "MX record" "security" .cindex "DNSSEC" "MX lookup" .cindex "security" "MX lookup" .cindex "DNS" "DNSSEC" DNS lookups for domains matching &%dnssec_request_domains%& will be done with -the dnssec request bit set. -This applies to all of the SRV, MX, AAAA, A lookup sequence. +the dnssec request bit set. Setting this transport option is only useful if the +transport overrides or sets the host names. See the &%dnssec_request_domains%& +router option. @@ -24298,9 +24609,9 @@ This applies to all of the SRV, MX, AAAA, A lookup sequence. .cindex "security" "MX lookup" .cindex "DNS" "DNSSEC" DNS lookups for domains matching &%dnssec_require_domains%& will be done with -the dnssec request bit set. Any returns not having the Authenticated Data bit -(AD bit) set will be ignored and logged as a host-lookup failure. -This applies to all of the SRV, MX, AAAA, A lookup sequence. +the dnssec request bit set. Setting this transport option is only +useful if the transport overrides or sets the host names. See the +&%dnssec_require_domains%& router option. @@ -24445,6 +24756,32 @@ facilities such as AUTH, PIPELINING, SIZE, and STARTTLS. Exim will not use the SMTP PIPELINING extension when delivering to any host that matches this list, even if the server host advertises PIPELINING support. +.new +.option hosts_pipe_connect smtp "host list&!!" unset +.cindex "pipelining" "early connection" +.cindex "pipelining" PIPE_CONNECT +If Exim is built with the SUPPORT_PIPE_CONNECT build option +this option controls which to hosts the facility watched for +and recorded, and used for subsequent connections. + +The retry hints database is used for the record, +and records are subject to the &%retry_data_expire%& option. +When used, the pipelining saves on roundtrip times. +It also turns SMTP into a client-first protocol +so combines well with TCP Fast Open. + +See also the &%pipelining_connect_advertise_hosts%& main option. + +Note: +When the facility is used, the transport &%helo_data%& option +will be expanded before the &$sending_ip_address$& variable +is filled in. +A check is made for the use of that variable, without the +presence of a &"def:"& test on it, but suitably complex coding +can avoid the check and produce unexpected results. +You have been warned. +.wen + .option hosts_avoid_tls smtp "host list&!!" unset .cindex "TLS" "avoiding for certain hosts" @@ -24484,13 +24821,15 @@ been started will not be passed to a new delivery process for sending another message on the same connection. See section &<>& for an explanation of when this might be needed. -.option hosts_noproxy_tls smtp "host list&!!" * +.new +.option hosts_noproxy_tls smtp "host list&!!" unset .cindex "TLS" "passing connection" .cindex "multiple SMTP deliveries" .cindex "TLS" "multiple message deliveries" For any host that matches this list, a TLS session which has been started will not be passed to a new delivery process for sending another message on the same session. +.wen The traditional implementation closes down TLS and re-starts it in the new process, on the same open TCP connection, for each successive message @@ -24553,7 +24892,8 @@ TLS session for any host that matches this list. .cindex DANE "requiring for certain servers" If built with DANE support, Exim will require that a DNSSEC-validated TLSA record is present for any host matching the list, -and that a DANE-verified TLS connection is made. +and that a DANE-verified TLS connection is made. See +the &%dnssec_request_domains%& router and transport options. There will be no fallback to in-clear communication. See section &<>&. @@ -24586,17 +24926,17 @@ This option provides a list of servers to which, provided they announce CHUNKING support, Exim will attempt to use BDAT commands rather than DATA. BDAT will not be used in conjunction with a transport filter. -.option hosts_try_dane smtp "host list&!!" unset +.option hosts_try_dane smtp "host list&!!" * .cindex DANE "transport options" .cindex DANE "attempting for certain servers" -If built with DANE support, Exim will lookup a -TLSA record for any host matching the list. -If found and verified by DNSSEC, -a DANE-verified TLS connection is made to that host; -there will be no fallback to in-clear communication. +If built with DANE support, Exim will require that a DNSSEC-validated +TLSA record is present for any host matching the list, +and that a DANE-verified TLS connection is made. See +the &%dnssec_request_domains%& router and transport options. +There will be no fallback to in-clear communication. See section &<>&. -.option hosts_try_fastopen smtp "host list&!!" unset +.option hosts_try_fastopen smtp "host list&!!" * .cindex "fast open, TCP" "enabling, in client" .cindex "TCP Fast Open" "enabling, in client" .cindex "RFC 7413" "TCP Fast Open" @@ -24710,10 +25050,8 @@ and if &%protocol%& is set to &"smtps"& the default is &"smtps"&. If the expansion fails, or if a port number cannot be found, delivery is deferred. -.new Note that at least one Linux distribution has been seen failing to put &"smtps"& in its &"/etc/services"& file, resulting is such deferrals. -.wen @@ -24731,11 +25069,9 @@ over a pipe to a local process &-- see chapter &<>&. If this option is set to &"smtps"&, the default value for the &%port%& option changes to &"smtps"&, and the transport initiates TLS immediately after connecting, as an outbound SSL-on-connect, instead of using STARTTLS to upgrade. -.new The Internet standards bodies used to strongly discourage use of this mode, but as of RFC 8314 it is perferred over STARTTLS for message submission (as distinct from MTA-MTA communication). -.wen .option retry_include_ip_address smtp boolean&!! true @@ -24964,7 +25300,6 @@ The &%tls_verify_certificates%& option must also be set. If both this option and &%tls_try_verify_hosts%& are unset operation is as if this option selected all hosts. -.new .option utf8_downconvert smtp integer!! unset .cindex utf8 "address downconversion" .cindex i18n "utf8 address downconversion" @@ -24972,7 +25307,6 @@ If built with internationalization support, this option controls conversion of UTF-8 in message addresses to a-label form. For details see section &<>&. -.wen @@ -25165,6 +25499,7 @@ When an address is being routed, either for delivery or for verification, rewriting is applied immediately to child addresses that are generated by redirection, unless &%no_rewrite%& is set on the router. +.cindex "envelope from" .cindex "envelope sender" "rewriting at transport time" .cindex "rewriting" "at transport time" .cindex "header lines" "rewriting at transport time" @@ -26133,6 +26468,7 @@ included by setting AUTH_CRAM_MD5=yes AUTH_CYRUS_SASL=yes AUTH_DOVECOT=yes +AUTH_EXTERNAL=yes AUTH_GSASL=yes AUTH_HEIMDAL_GSSAPI=yes AUTH_PLAINTEXT=yes @@ -26144,15 +26480,20 @@ authentication mechanism (RFC 2195), and the second provides an interface to the Cyrus SASL authentication library. The third is an interface to Dovecot's authentication system, delegating the work via a socket interface. -The fourth provides an interface to the GNU SASL authentication library, which +.new +The fourth provides for negotiation of authentication done via non-SMTP means, +as defined by RFC 4422 Appendix A. +.wen +The fifth provides an interface to the GNU SASL authentication library, which provides mechanisms but typically not data sources. -The fifth provides direct access to Heimdal GSSAPI, geared for Kerberos, but +The sixth provides direct access to Heimdal GSSAPI, geared for Kerberos, but supporting setting a server keytab. -The sixth can be configured to support +The seventh can be configured to support the PLAIN authentication mechanism (RFC 2595) or the LOGIN mechanism, which is -not formally documented, but used by several MUAs. The seventh authenticator +not formally documented, but used by several MUAs. +The eighth authenticator supports Microsoft's &'Secure Password Authentication'& mechanism. -The eighth is an Exim authenticator but not an SMTP one; +The last is an Exim authenticator but not an SMTP one; instead it can use information from a TLS negotiation. The authenticators are configured using the same syntax as other drivers (see @@ -26431,7 +26772,7 @@ no successful authentication. .cindex authentication "expansion item" Successful authentication sets up information used by the -&$authresults$& expansion item. +&%authresults%& expansion item. @@ -27387,6 +27728,143 @@ msn: +. //////////////////////////////////////////////////////////////////////////// +. //////////////////////////////////////////////////////////////////////////// + +.chapter "The external authenticator" "CHAPexternauth" +.scindex IIDexternauth1 "&(external)& authenticator" +.scindex IIDexternauth2 "authenticators" "&(external)&" +.cindex "authentication" "Client Certificate" +.cindex "authentication" "X509" +.cindex "Certificate-based authentication" +The &(external)& authenticator provides support for +authentication based on non-SMTP information. +The specification is in RFC 4422 Appendix A +(&url(https://tools.ietf.org/html/rfc4422)). +It is only a transport and negotiation mechanism; +the process of authentication is entirely controlled +by the server configuration. + +The client presents an identity in-clear. +It is probably wise for a server to only advertise, +and for clients to only attempt, +this authentication method on a secure (eg. under TLS) connection. + +One possible use, compatible with the +K-9 Mail Andoid client (&url(https://k9mail.github.io/)), +is for using X509 client certificates. + +It thus overlaps in function with the TLS authenticator +(see &<>&) +but is a full SMTP SASL authenticator +rather than being implicit for TLS-connection carried +client certificates only. + +The examples and discussion in this chapter assume that +client-certificate authentication is being done. + +The client must present a certificate, +for which it must have been requested via the +&%tls_verify_hosts%& or &%tls_try_verify_hosts%& main options +(see &<>&). +For authentication to be effective the certificate should be +verifiable against a trust-anchor certificate known to the server. + +.section "External options" "SECTexternsoptions" +.cindex "options" "&(external)& authenticator (server)" +The &(external)& authenticator has two server options: + +.option server_param2 external string&!! unset +.option server_param3 external string&!! unset +.cindex "variables (&$auth1$& &$auth2$& etc)" "in &(external)& authenticator" +These options are expanded before the &%server_condition%& option +and the result are placed in &$auth2$& and &$auth3$& resectively. +If the expansion is forced to fail, authentication fails. Any other expansion +failure causes a temporary error code to be returned. + +They can be used to clarify the coding of a complex &%server_condition%&. + +.section "Using external in a server" "SECTexternserver" +.cindex "AUTH" "in &(external)& authenticator" +.cindex "numerical variables (&$1$& &$2$& etc)" &&& + "in &(external)& authenticator" +.vindex "&$auth1$&, &$auth2$&, etc" +.cindex "base64 encoding" "in &(external)& authenticator" + +When running as a server, &(external)& performs the authentication test by +expanding a string. The data sent by the client with the AUTH command, or in +response to subsequent prompts, is base64 encoded, and so may contain any byte +values when decoded. The decoded value is treated as +an identity for authentication and +placed in the expansion variable &$auth1$&. + +For compatibility with previous releases of Exim, the value is also placed in +the expansion variable &$1$&. However, the use of this +variable for this purpose is now deprecated, as it can lead to confusion in +string expansions that also use them for other things. + +.vindex "&$authenticated_id$&" +Once an identity has been received, +&%server_condition%& is expanded. If the expansion is forced to fail, +authentication fails. Any other expansion failure causes a temporary error code +to be returned. If the result of a successful expansion is an empty string, +&"0"&, &"no"&, or &"false"&, authentication fails. If the result of the +expansion is &"1"&, &"yes"&, or &"true"&, authentication succeeds and the +generic &%server_set_id%& option is expanded and saved in &$authenticated_id$&. +For any other result, a temporary error code is returned, with the expanded +string as the error text. + +Example: +.code +ext_ccert_san_mail: + driver = external + public_name = EXTERNAL + + server_advertise_condition = $tls_in_certificate_verified + server_param2 = ${certextract {subj_altname,mail,>:} \ + {$tls_in_peercert}} + server_condition = ${if forany {$auth2} \ + {eq {$item}{$auth1}}} + server_set_id = $auth1 +.endd +This accepts a client certificate that is verifiable against any +of your configured trust-anchors +(which usually means the full set of public CAs) +and which has a mail-SAN matching the claimed identity sent by the client. + +Note that, up to TLS1.2, the client cert is on the wire in-clear, including the SAN, +The account name is therefore guessable by an opponent. +TLS 1.3 protects both server and client certificates, and is not vulnerable +in this way. +Likewise, a traditional plaintext SMTP AUTH done inside TLS is not. + + +.section "Using external in a client" "SECTexternclient" +.cindex "options" "&(external)& authenticator (client)" +The &(external)& authenticator has one client option: + +.option client_send external string&!! unset +This option is expanded and sent with the AUTH command as the +identity being asserted. + +Example: +.code +ext_ccert: + driver = external + public_name = EXTERNAL + + client_condition = ${if !eq{$tls_out_cipher}{}} + client_send = myaccount@smarthost.example.net +.endd + + +.ecindex IIDexternauth1 +.ecindex IIDexternauth2 + + + + + . //////////////////////////////////////////////////////////////////////////// . //////////////////////////////////////////////////////////////////////////// @@ -27577,11 +28055,8 @@ to use GnuTLS, you need to set .code USE_GNUTLS=yes .endd -in Local/Makefile, in addition to -.code -SUPPORT_TLS=yes -.endd -You must also set TLS_LIBS and TLS_INCLUDE appropriately, so that the +in Local/Makefile +you must also set TLS_LIBS and TLS_INCLUDE appropriately, so that the include files and libraries for GnuTLS can be found. There are some differences in usage when using GnuTLS instead of OpenSSL: @@ -27715,9 +28190,7 @@ the size of the generated prime, so it might still be too large. .oindex "&%tls_require_ciphers%&" "OpenSSL" There is a function in the OpenSSL library that can be passed a list of cipher suites before the cipher negotiation takes place. This specifies which ciphers -.new are acceptable for TLS versions prior to 1.3. -.wen The list is colon separated and may contain names like DES-CBC3-SHA. Exim passes the expanded value of &%tls_require_ciphers%& directly to this function call. @@ -27783,7 +28256,6 @@ This example will prefer ECDSA-authenticated ciphers over RSA ones: tls_require_ciphers = ECDSA:RSA:!COMPLEMENTOFDEFAULT .endd -.new For TLS version 1.3 the control available is less fine-grained and Exim does not provide access to it at present. The value of the &%tls_require_ciphers%& option is ignored when @@ -27793,7 +28265,6 @@ As of writing the library default cipher suite list for TLSv1.3 is .code TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256 .endd -.wen .section "Requiring specific ciphers or other parameters in GnuTLS" &&& @@ -28102,7 +28573,7 @@ There is no current way to staple a proof for a client certificate. -.section "Configuring an Exim client to use TLS" "SECID185" +.section "Configuring an Exim client to use TLS" "SECTclientTLS" .cindex "cipher" "logging" .cindex "log" "TLS cipher" .cindex "log" "distinguished name" @@ -28142,6 +28613,13 @@ transport provide the client with a certificate, which is passed to the server if it requests it. If the server is Exim, it will request a certificate only if &%tls_verify_hosts%& or &%tls_try_verify_hosts%& matches the client. +.new +Do not use a certificate which has the OCSP-must-staple extension, +for client use (they are usable for server use). +As TLS has no means for the client to staple before TLS 1.3 it will result +in failed connections. +.wen + If the &%tls_verify_certificates%& option is set on the &(smtp)& transport, it specifies a collection of expected server certificates. These may be @@ -28265,7 +28743,7 @@ Great care should be taken to deal with matters of case, various injection attacks in the string (&`../`& or SQL), and ensuring that a valid filename can always be referenced; it is important to remember that &$tls_in_sni$& is arbitrary unverified data provided prior to authentication. -Further, the initial certificate is loaded before SNI is arrived, so +Further, the initial certificate is loaded before SNI has arrived, so an expansion for &%tls_certificate%& must have a default which is used when &$tls_in_sni$& is empty. @@ -28460,7 +28938,12 @@ Support for client-side operation of DANE can be included at compile time by def in &_Local/Makefile_&. If it has been included, the macro "_HAVE_DANE" will be defined. -The TLSA record for the server may have "certificate usage" of DANE-TA(2) or DANE-EE(3). +A TLSA record consist of 4 fields, the "Certificate Usage", the +"Selector", the "Matching type", and the "Certificate Association Data". +For a detailed description of the TLSA record see +&url(https://tools.ietf.org/html/rfc7671#page-5,RFC 7671). + +The TLSA record for the server may have "Certificate Usage" (1st) field of DANE-TA(2) or DANE-EE(3). These are the "Trust Anchor" and "End Entity" variants. The latter specifies the End Entity directly, i.e. the certificate involved is that of the server (and if only DANE-EE is used then it should be the sole one transmitted during the TLS handshake); @@ -28476,7 +28959,6 @@ DANE-TA is commonly used for several services and/or servers, each having a TLSA all of which point to a single TLSA record. DANE-TA and DANE-EE can both be used together. -.new Our recommendation is to use DANE with a certificate from a public CA, because this enables a variety of strategies for remote clients to verify your certificate. @@ -28501,25 +28983,33 @@ The list of requirements is subject to change as best practices evolve. If you're not already using a private CA, or it doesn't meet these requirements, then we encourage you to avoid all these issues and use a public CA such as &url(https://letsencrypt.org/,Let's Encrypt) instead. -.wen -The TLSA record should have a Selector field of SPKI(1) and a Matching Type field of SHA2-512(2). +The TLSA record should have a "Selector" (2nd) field of SPKI(1) and +a "Matching Type" (3rd) field of SHA2-512(2). -At the time of writing, &url(https://www.huque.com/bin/gen_tlsa) -is useful for quickly generating TLSA records; and commands like +For the "Certificate Authority Data" (4th) field, commands like .code - openssl x509 -in -pubkey -noout /dev/null \ | openssl sha512 \ | awk '{print $2}' .endd -are workable for 4th-field hashes. +are workable to create a hash of the certificate's public key. + +An example TLSA record for DANE-EE(3), SPKI(1), and SHA-512 (2) looks like + +.code + _25._tcp.mail.example.com. TLSA 3 1 2 8BA8A336E... +.endd + +At the time of writing, &url(https://www.huque.com/bin/gen_tlsa) +is useful for quickly generating TLSA records. + For use with the DANE-TA model, server certificates must have a correct name (SubjectName or SubjectAltName). -.new The Certificate issued by the CA published in the DANE-TA model should be issued using a strong hash algorithm. Exim, and importantly various other MTAs sending to you, will not @@ -28527,7 +29017,6 @@ re-enable hash algorithms which have been disabled by default in TLS libraries. This means no MD5 and no SHA-1. SHA2-256 is the minimum for reliable interoperability (and probably the maximum too, in 2018). -.wen The use of OCSP-stapling should be considered, allowing for fast revocation of certificates (which would otherwise be limited by the DNS TTL on the TLSA records). However, this is likely to only be usable with DANE-TA. NOTE: the @@ -28551,7 +29040,9 @@ those who use &%hosts_require_ocsp%&, should consider the interaction with DANE For client-side DANE there are three new smtp transport options, &%hosts_try_dane%&, &%hosts_require_dane%& and &%dane_require_tls_ciphers%&. -The require variant will result in failure if the target host is not DNSSEC-secured. +The require variant will result in failure if the target host is not +DNSSEC-secured. To get DNSSEC-secured hostname resolution, use +the &%dnssec_request_domains%& router or transport option. DANE will only be usable if the target host has DNSSEC-secured MX, A and TLSA records. @@ -28581,7 +29072,8 @@ If DANE is requested and useable (see above) the following transport options are If DANE is not usable, whether requested or not, and CA-anchored verification evaluation is wanted, the above variables should be set appropriately. -Currently the &%dnssec_request_domains%& must be active and &%dnssec_require_domains%& is ignored. +The router and transport option &%dnssec_request_domains%& must not be +set to "never" and &%dnssec_require_domains%& is ignored. If verification was successful using DANE then the "CV" item in the delivery log line will show as "CV=dane". @@ -30464,7 +30956,9 @@ the next &%local_parts%& test. .cindex "&ACL;" "virus scanning" .cindex "&ACL;" "scanning for viruses" This condition is available only when Exim is compiled with the -content-scanning extension. It causes the incoming message to be scanned for +content-scanning extension +and only after a DATA command. +It causes the incoming message to be scanned for viruses. For details, see chapter &<>&. .vitem &*mime_regex&~=&~*&<&'list&~of&~regular&~expressions'&> @@ -30625,13 +31119,13 @@ client host, and its contents have been verified. If there has been no previous attempt to verify the HELO/EHLO contents, it is carried out when this condition is encountered. See the description of the &%helo_verify_hosts%& and &%helo_try_verify_hosts%& options for details of how to request verification -independently of this condition. +independently of this condition, and for detail of the verification. For SMTP input that does not come over TCP/IP (the &%-bs%& command line option), this condition is always true. -.vitem &*verify&~=&~not_blind*& +.vitem &*verify&~=&~not_blind/*&<&'options'&> .cindex "verifying" "not blind" .cindex "bcc recipients, verifying none" This condition checks that there are no blind (bcc) recipients in the message. @@ -30641,6 +31135,11 @@ case-sensitively; domains are checked case-insensitively. If &'Resent-To:'& or &'Resent-Cc:'& header lines exist, they are also checked. This condition can be used only in a DATA or non-SMTP ACL. +.new +There is one possible option, &`case_insensitive`&. If this is present then +local parts are checked case-insensitively. +.wen + There are, of course, many legitimate messages that make use of blind (bcc) recipients. This check should not be used on its own for blocking messages. @@ -31368,14 +31867,12 @@ rest of the ACL. The &%leaky%& (default) option means that the client's recorded rate is not updated if it is above the limit. The effect of this is that Exim measures the client's average rate of successfully sent email, -.new up to the given limit. This is appropriate if the countermeasure when the condition is true consists of refusing the message, and is generally the better choice if you have clients that retry automatically. If the action when true is anything more complex then this option is likely not what is wanted. -.wen The &%strict%& option means that the client's recorded rate is always updated. The effect of this is that Exim measures the client's average rate @@ -31546,14 +32043,12 @@ connection, HELO, or MAIL). The main use of these variables is expected to be to distinguish between rejections of MAIL and rejections of RCPT in callouts. -.new The above variables may also be set after a &*successful*& address verification to: .ilist &%random%&: A random local-part callout succeeded .endlist -.wen @@ -32251,6 +32746,15 @@ It supports a &"generic"& interface to scanners called via the shell, and specialized interfaces for &"daemon"& type virus scanners, which are resident in memory and thus are much faster. +.new +Since message data needs to have arrived, +the condition may be only called in ACL defined by +&%acl_smtp_data%&, +&%acl_smtp_data_prdr%&, +&%acl_smtp_mime%& or +&%acl_smtp_dkim%& +.wen + A timeout of 2 minutes is applied to a scanner call (by default); if it expires then a defer action is taken. @@ -32642,7 +33146,7 @@ intend to use an instance running on the local host you do not need to set you must set the &%spamd_address%& option in the global part of the Exim configuration as follows (example): .code -spamd_address = 192.168.99.45 387 +spamd_address = 192.168.99.45 783 .endd The SpamAssassin protocol relies on a TCP half-close from the client. If your SpamAssassin client side is running a Linux system with an @@ -33151,9 +33655,7 @@ code. The incident is logged on the main and reject logs. .cindex "&[local_scan()]& function" "building Exim to use" To make use of the local scan function feature, you must tell Exim where your function is before building Exim, by setting -.new both HAVE_LOCAL_SCAN and -.wen LOCAL_SCAN_SOURCE in your &_Local/Makefile_&. A recommended place to put it is in the &_Local_& directory, so you might set @@ -34134,6 +34636,7 @@ headers remove "Old-Subject" .section "Setting an errors address in a system filter" "SECID217" +.cindex "envelope from" .cindex "envelope sender" In a system filter, if a &%deliver%& command is followed by .code @@ -34367,6 +34870,7 @@ other words, such qualification is also controlled by .cindex "sender" "address" .oindex "&%uucp_from_pattern%&" .oindex "&%uucp_from_sender%&" +.cindex "envelope from" .cindex "envelope sender" .cindex "Sendmail compatibility" "&""From""& line" Messages that have come from UUCP (and some other applications) often begin @@ -35815,6 +36319,7 @@ the address, giving a suitable error message. .section "Variable Envelope Return Paths (VERP)" "SECTverp" .cindex "VERP" .cindex "Variable Envelope Return Paths" +.cindex "envelope from" .cindex "envelope sender" Variable Envelope Return Paths &-- see &url(https://cr.yp.to/proto/verp.txt) &-- are a way of helping mailing list administrators discover which subscription @@ -36806,7 +37311,7 @@ the following table: &`F `& sender address (on delivery lines) &`H `& host name and IP address &`I `& local interface used -&`id `& message id for incoming message +&`id `& message id (from header) for incoming message &`K `& CHUNKING extension used &`L `& on &`<=`& and &`=>`& lines: PIPELINING extension used &`M8S `& 8BITMIME status for incoming message @@ -36913,6 +37418,8 @@ selection marked by asterisks: &` incoming_port `& remote port on <= lines &`*lost_incoming_connection `& as it says (includes timeouts) &` millisec `& millisecond timestamps and RT,QT,DT,D times +&`*msg_id `& on <= lines, Message-ID: header value +&` msg_id_created `& on <= lines, Message-ID: header value when one had to be added &` outgoing_interface `& local interface on => lines &` outgoing_port `& add remote port to => lines &`*queue_run `& start and end queue runs @@ -37096,6 +37603,16 @@ connection is unexpectedly dropped. &%millisec%&: Timestamps have a period and three decimal places of finer granularity appended to the seconds value. .next +.new +.cindex "log" "message id" +&%msg_id%&: The value of the Message-ID: header. +.next +&%msg_id_created%&: The value of the Message-ID: header, when one had to be created. +This will be either because the message is a bounce, or was submitted locally +(submission mode) without one. +The field identifier will have an asterix appended: &"id*="&. +.wen +.next .cindex "log" "outgoing interface" .cindex "log" "local interface" .cindex "log" "local address and port" @@ -37122,7 +37639,6 @@ local port is a random ephemeral port. &%pid%&: The current process id is added to every log line, in square brackets, immediately after the time and date. .next -.new .cindex log pipelining .cindex pipelining "logging outgoing" &%pipelining%&: A field is added to delivery and accept @@ -37131,6 +37647,15 @@ The field is a single "L". On accept lines, where PIPELINING was offered but not used by the client, the field has a minus appended. + +.new +.cindex "pipelining" "early connection" +If Exim is built with the SUPPORT_PIPE_CONNECT build option +accept "L" fields have a period appended if the feature was +offered but not used, or an asterisk appended if used. +Delivery "L" fields have an asterisk appended if used. +.wen + .next .cindex "log" "queue run" .cindex "queue runner" "logging" @@ -37486,6 +38011,11 @@ Match only frozen messages. .vitem &*-x*& Match only non-frozen messages. + +.new +.vitem &*-G*&&~<&'queuename'&> +Match only messages in the given queue. Without this, the default queue is searched. +.wen .endlist The following options control the format of the output: @@ -38951,11 +39481,9 @@ two files contains the final component of its own name as its first line. This is insurance against disk crashes where the directory is lost but the files themselves are recoverable. -.new The file formats may be changed, or new formats added, at any release. Spool files are not intended as an interface to other programs and should not be used as such. -.wen Some people are tempted into editing -D files in order to modify messages. You need to be extremely careful if you do this; it is not recommended and you are @@ -39175,6 +39703,11 @@ was received from the client, this records the Distinguished Name from that certificate. .endlist +.new +Any of the above may have an extra hyphen prepended, to indicate the the +corresponding data is untrusted. +.wen + Following the options there is a list of those addresses to which the message is not to be delivered. This set of addresses is initialized from the command line when the &%-t%& option is used and &%extract_addresses_remove_arguments%& @@ -39283,11 +39816,11 @@ There is no dot-stuffing (and no dot-termination). . //////////////////////////////////////////////////////////////////////////// . //////////////////////////////////////////////////////////////////////////// -.chapter "DKIM and SPF" "CHAPdkim" &&& - "DKIM and SPF Support" -.cindex "DKIM" +.chapter "DKIM, SPF and DMARC" "CHAPdkim" &&& + "DKIM, SPF and DMARC Support" .section "DKIM (DomainKeys Identified Mail)" SECDKIM +.cindex "DKIM" DKIM is a mechanism by which messages sent by some entity can be provably linked to a domain which that entity controls. It permits reputation to @@ -39342,7 +39875,7 @@ senders). .cindex "DKIM" "signing" For signing to be usable you must have published a DKIM record in DNS. -Note that RFC 8301 says: +Note that RFC 8301 (which does not cover EC keys) says: .code rsa-sha1 MUST NOT be used for signing or verifying. @@ -39362,7 +39895,11 @@ These options take (expandable) strings as arguments. .option dkim_domain smtp string list&!! unset The domain(s) you want to sign with. After expansion, this can be a list. -Each element in turn is put into the &%$dkim_domain%& expansion variable +Each element in turn, +.new +lowercased, +.wen +is put into the &%$dkim_domain%& expansion variable while expanding the remaining signing options. If it is empty after expansion, DKIM signing is not done, and no error will result even if &%dkim_strict%& is set. @@ -39416,8 +39953,9 @@ Signers MUST use RSA keys of at least 1024 bits for all keys. Signers SHOULD use RSA keys of at least 2048 bits. .endd -Support for EC keys is being developed under -&url(https://datatracker.ietf.org/doc/draft-ietf-dcrup-dkim-crypto/). +.new +EC keys for DKIM are defined by RFC 8463. +.wen They are considerably smaller than RSA keys for equivalent protection. As they are a recent development, users should consider dual-signing (by setting a list of selectors, and an expansion for this option) @@ -39437,10 +39975,12 @@ openssl pkey -outform DER -pubout -in dkim_ed25519.private | tail -c +13 | base6 certtool --load_privkey=dkim_ed25519.private --pubkey_info --outder | tail -c +13 | base64 .endd -Note that the format -of Ed25519 keys in DNS has not yet been decided; this release supports -both of the leading candidates at this time, a future release will -probably drop support for whichever proposal loses. +.new +Exim also supports an alternate format +of Ed25519 keys in DNS which was a candidate during development +of the standard, but not adopted. +A future release will probably drop that support. +.wen .option dkim_hash smtp string&!! sha256 Can be set to any one of the supported hash methods, which are: @@ -39498,7 +40038,6 @@ If a '+' prefix if used, all headers that are present with this name will be signed, and one signature added for a missing header with the name will be appended. -.new .option dkim_timestamps smtp integer&!! unset This option controls the inclusion of timestamp information in the signature. If not set, no such information will be included. @@ -39508,40 +40047,50 @@ for the expiry tag both creation (t=) and expiry (x=) tags will be included. RFC 6376 lists these tags as RECOMMENDED. -.wen .section "Verifying DKIM signatures in incoming mail" "SECDKIMVFY" .cindex "DKIM" "verification" -.new Verification of DKIM signatures in SMTP incoming email is done for all messages for which an ACL control &%dkim_disable_verify%& has not been set. +.new +.cindex DKIM "selecting signature algorithms" +Individual classes of signature algorithm can be ignored by changing +the main options &%dkim_verify_hashes%& or &%dkim_verify_keytypes%&. +The &%dkim_verify_minimal%& option can be set to cease verification +processing for a message once the first passing signature is found. +.wen + .cindex authentication "expansion item" Performing verification sets up information used by the -&$authresults$& expansion item. +&%authresults%& expansion item. + +.new +For most purposes the default option settings suffice and the remainder +of this section can be ignored. .wen -.new The results of that verification are then made available to the -&%acl_smtp_dkim%& ACL, &new(which can examine and modify them). -By default, this ACL is called once for each -syntactically(!) correct signature in the incoming message. +The results of verification are made available to the +&%acl_smtp_dkim%& ACL, which can examine and modify them. A missing ACL definition defaults to accept. +By default, the ACL is called once for each +syntactically(!) correct signature in the incoming message. If any ACL call does not accept, the message is not accepted. If a cutthrough delivery was in progress for the message, that is summarily dropped (having wasted the transmission effort). -To evaluate the &new(verification result) in the ACL +To evaluate the verification result in the ACL a large number of expansion variables containing the signature status and its details are set up during the runtime of the ACL. Calling the ACL only for existing signatures is not sufficient to build -more advanced policies. For that reason, the global option -&%dkim_verify_signers%&, and a global expansion variable +more advanced policies. For that reason, the main option +&%dkim_verify_signers%&, and an expansion variable &%$dkim_signers%& exist. -The global option &%dkim_verify_signers%& can be set to a colon-separated +The main option &%dkim_verify_signers%& can be set to a colon-separated list of DKIM domains or identities for which the ACL &%acl_smtp_dkim%& is called. It is expanded when the message has been received. At this point, the expansion variable &%$dkim_signers%& already contains a colon-separated @@ -39567,11 +40116,19 @@ dkim_verify_signers = $sender_address_domain:$dkim_signers If a domain or identity is listed several times in the (expanded) value of &%dkim_verify_signers%&, the ACL is only called once for that domain or identity. +.new +Note that if the option is set using untrustworthy data +(such as the From: header) +care should be taken to force lowercase for domains +and for the domain part if identities. +The default setting can be regarded as trustworthy in this respect. +.wen + If multiple signatures match a domain (or identity), the ACL is called once for each matching signature. -Inside the &%acl_smtp_dkim%&, the following expansion variables are +Inside the DKIM ACL, the following expansion variables are available (from most to least important): @@ -39665,8 +40222,12 @@ DKIM signatures identified as having been signed with historic algorithms (currently, rsa-sha1) have permanently failed evaluation .endd -To enforce this you must have a DKIM ACL which checks this variable -and overwrites the &$dkim_verify_status$& variable as discussed above. +To enforce this you must either have a DKIM ACL which checks this variable +and overwrites the &$dkim_verify_status$& variable as discussed above, +.new +or have set the main option &%dkim_verify_hashes%& to exclude +processing of such signatures. +.wen .vitem &%$dkim_canon_body%& The body canonicalization method. One of 'relaxed' or 'simple'. @@ -39685,12 +40246,10 @@ strict enforcement should code the check explicitly. The number of signed body bytes. If zero ("0"), the body is unsigned. If no limit was set by the signer, "9999999999999" is returned. This makes sure that this variable always expands to an integer value. -.new &*Note:*& The presence of the signature tag specifying a signing body length is one possible route to spoofing of valid DKIM signatures. A paranoid implementation might wish to regard signature where this variable shows less than the "no limit" return as being invalid. -.wen .vitem &%$dkim_created%& UNIX timestamp reflecting the date and time when the signature was created. @@ -39783,8 +40342,12 @@ for more information of what they mean. SPF is a mechanism whereby a domain may assert which IP addresses may transmit messages with its domain in the envelope from, documented by RFC 7208. -For more information on SPF see &url(http://www.openspf.org). -. --- 2018-09-07: still not https +For more information on SPF see &url(http://www.open-spf.org), a static copy of +the &url(http://openspf.org). +. --- 2019-10-28: still not https, open-spf.org is told to be a +. --- web-archive copy of the now dead openspf.org site +. --- See https://www.mail-archive.com/mailop@mailop.org/msg08019.html for a +. --- discussion. Messages sent by a system not authorised will fail checking of such assertions. This includes retransmissions done by traditional forwarders. @@ -39798,7 +40361,7 @@ publishing certain DNS records is all that is required. For verification, an ACL condition and an expansion lookup are provided. .cindex authentication "expansion item" Performing verification sets up information used by the -&$authresults$& expansion item. +&%authresults%& expansion item. .cindex SPF "ACL condition" @@ -39847,7 +40410,7 @@ deny spf = fail message = $sender_host_address is not allowed to send mail from \ ${if def:sender_address_domain \ {$sender_address_domain}{$sender_helo_name}}. \ - Please see http://www.openspf.org/Why?scope=\ + Please see http://www.open-spf.org/Why?scope=\ ${if def:sender_address_domain {mfrom}{helo}};\ identity=${if def:sender_address_domain \ {$sender_address}{$sender_helo_name}};\ @@ -39900,9 +40463,9 @@ In addition to SPF, you can also perform checks for so-called "Best-guess". Strictly speaking, "Best-guess" is not standard SPF, but it is supported by the same framework that enables SPF capability. -Refer to &url(http://www.openspf.org/FAQ/Best_guess_record) +Refer to &url(http://www.open-spf.org/FAQ/Best_guess_record) for a description of what it means. -. --- 2018-09-07: still not https: +. --- 2019-10-28: still not https: To access this feature, simply use the spf_guess condition in place of the spf one. For example: @@ -39935,7 +40498,11 @@ would relax host matching rules to a broader network range. .cindex SPF "lookup expansion" .cindex lookup spf A lookup expansion is also available. It takes an email -address as the key and an IP address as the database: +address as the key and an IP address +.new +(v4 or v6) +.wen +as the database: .code ${lookup {username@domain} spf {ip.ip.ip.ip}} @@ -39943,7 +40510,241 @@ address as the key and an IP address as the database: The lookup will return the same result strings as can appear in &$spf_result$& (pass,fail,softfail,neutral,none,err_perm,err_temp). -Currently, only IPv4 addresses are supported. + + + + + +.new +.section DMARC SECDMARC +.cindex DMARC verification + +DMARC combines feedback from SPF, DKIM, and header From: in order +to attempt to provide better indicators of the authenticity of an +email. This document does not explain the fundamentals; you +should read and understand how it works by visiting the website at +&url(http://www.dmarc.org/). + +If Exim is built with DMARC support, +the libopendmarc library is used. + +For building Exim yourself, obtain the library from +&url(http://sourceforge.net/projects/opendmarc/) +to obtain a copy, or find it in your favorite rpm package +repository. You will need to attend to the local/Makefile feature +SUPPORT_DMARC and the associated LDFLAGS addition. +This description assumes +that headers will be in /usr/local/include, and that the libraries +are in /usr/local/lib. + +. subsection + +There are three main-configuration options: +.cindex DMARC "configuration options" + +The &%dmarc_tld_file%& option +.oindex &%dmarc_tld_file%& +defines the location of a text file of valid +top level domains the opendmarc library uses +during domain parsing. Maintained by Mozilla, +the most current version can be downloaded +from a link at &url(https://publicsuffix.org/list/, currently pointing +at https://publicsuffix.org/list/public_suffix_list.dat) +See also util/renew-opendmarc-tlds.sh script. +The default for the option is /etc/exim/opendmarc.tlds. + + +The &%dmarc_history_file%& option, if set +.oindex &%dmarc_history_file%& +defines the location of a file to log results +of dmarc verification on inbound emails. The +contents are importable by the opendmarc tools +which will manage the data, send out DMARC +reports, and expire the data. Make sure the +directory of this file is writable by the user +exim runs as. +The default is unset. + +The &%dmarc_forensic_sender%& option +.oindex &%dmarc_forensic_sender%& +defines an alternate email address to use when sending a +forensic report detailing alignment failures +if a sender domain's dmarc record specifies it +and you have configured Exim to send them. +If set, this is expanded and used for the +From: header line; the address is extracted +from it and used for the envelope from. +If not set (the default), the From: header is expanded from +the dsn_from option, and <> is used for the +envelope from. + +. I wish we had subsections... + +.cindex DMARC controls +By default, the DMARC processing will run for any remote, +non-authenticated user. It makes sense to only verify DMARC +status of messages coming from remote, untrusted sources. You can +use standard conditions such as hosts, senders, etc, to decide that +DMARC verification should *not* be performed for them and disable +DMARC with a control setting: +.code + control = dmarc_disable_verify +.endd +A DMARC record can also specify a "forensic address", which gives +exim an email address to submit reports about failed alignment. +Exim does not do this by default because in certain conditions it +results in unintended information leakage (what lists a user might +be subscribed to, etc). You must configure exim to submit forensic +reports to the owner of the domain. If the DMARC record contains a +forensic address and you specify the control statement below, then +exim will send these forensic emails. It's also advised that you +configure a dmarc_forensic_sender because the default sender address +construction might be inadequate. +.code + control = dmarc_enable_forensic +.endd +(AGAIN: You can choose not to send these forensic reports by simply +not putting the dmarc_enable_forensic control line at any point in +your exim config. If you don't tell it to send them, it will not +send them.) + +There are no options to either control. Both must appear before +the DATA acl. + +. subsection + +DMARC checks cam be run on incoming SMTP messages by using the +"dmarc_status" ACL condition in the DATA ACL. You are required to +call the "spf" condition first in the ACLs, then the "dmarc_status" +condition. Putting this condition in the ACLs is required in order +for a DMARC check to actually occur. All of the variables are set +up before the DATA ACL, but there is no actual DMARC check that +occurs until a "dmarc_status" condition is encountered in the ACLs. + +The dmarc_status condition takes a list of strings on its +right-hand side. These strings describe recommended action based +on the DMARC check. To understand what the policy recommendations +mean, refer to the DMARC website above. Valid strings are: +.display +&'accept '& The DMARC check passed and the library recommends accepting the email. +&'reject '& The DMARC check failed and the library recommends rejecting the email. +&'quarantine '& The DMARC check failed and the library recommends keeping it for further inspection. +&'none '& The DMARC check passed and the library recommends no specific action, neutral. +&'norecord '& No policy section in the DMARC record for this sender domain. +&'nofrom '& Unable to determine the domain of the sender. +&'temperror '& Library error or dns error. +&'off '& The DMARC check was disabled for this email. +.endd +You can prefix each string with an exclamation mark to invert its +meaning, for example "!accept" will match all results but +"accept". The string list is evaluated left-to-right in a +short-circuit fashion. When a string matches the outcome of the +DMARC check, the condition succeeds. If none of the listed +strings matches the outcome of the DMARC check, the condition +fails. + +Of course, you can also use any other lookup method that Exim +supports, including LDAP, Postgres, MySQL, etc, as long as the +result is a list of colon-separated strings. + +Performing the check sets up information used by the +&%authresults%& expansion item. + +Several expansion variables are set before the DATA ACL is +processed, and you can use them in this ACL. The following +expansion variables are available: + +&$dmarc_status$& +.vindex &$dmarc_status$& +.cindex DMARC result +is a one word status indicating what the DMARC library +thinks of the email. It is a combination of the results of +DMARC record lookup and the SPF/DKIM/DMARC processing results +(if a DMARC record was found). The actual policy declared +in the DMARC record is in a separate expansion variable. + +&$dmarc_status_text$& +.vindex &$dmarc_status_text$& +is a slightly longer, human readable status. + +&$dmarc_used_domain$& +.vindex &$dmarc_used_domain$& +is the domain which DMARC used to look up the DMARC policy record. + +&$dmarc_domain_policy$& +.vindex &$dmarc_domain_policy$& +is the policy declared in the DMARC record. Valid values +are "none", "reject" and "quarantine". It is blank when there +is any error, including no DMARC record. + +. subsection + +By default, Exim's DMARC configuration is intended to be +non-intrusive and conservative. To facilitate this, Exim will not +create any type of logging files without explicit configuration by +you, the admin. Nor will Exim send out any emails/reports about +DMARC issues without explicit configuration by you, the admin (other +than typical bounce messages that may come about due to ACL +processing or failure delivery issues). + +In order to log statistics suitable to be imported by the opendmarc +tools, you need to: +.ilist +Configure the global setting dmarc_history_file +.next +Configure cron jobs to call the appropriate opendmarc history +import scripts and truncating the dmarc_history_file +.endlist + +In order to send forensic reports, you need to: +.ilist +Configure the global setting dmarc_forensic_sender +.next +Configure, somewhere before the DATA ACL, the control option to +enable sending DMARC forensic reports +.endlist + +. subsection + +Example usage: +.code +(RCPT ACL) + warn domains = +local_domains + hosts = +local_hosts + control = dmarc_disable_verify + + warn !domains = +screwed_up_dmarc_records + control = dmarc_enable_forensic + + warn condition = (lookup if destined to mailing list) + set acl_m_mailing_list = 1 + +(DATA ACL) + warn dmarc_status = accept : none : off + !authenticated = * + log_message = DMARC DEBUG: $dmarc_status $dmarc_used_domain + + warn dmarc_status = !accept + !authenticated = * + log_message = DMARC DEBUG: '$dmarc_status' for $dmarc_used_domain + + warn dmarc_status = quarantine + !authenticated = * + set $acl_m_quarantine = 1 + # Do something in a transport with this flag variable + + deny condition = ${if eq{$dmarc_domain_policy}{reject}} + condition = ${if eq{$acl_m_mailing_list}{1}} + message = Messages from $dmarc_used_domain break mailing lists + + deny dmarc_status = reject + !authenticated = * + message = Message from $dmarc_used_domain failed sender's DMARC policy, REJECT + + warn add_header = :at_start:${authresults {$primary_hostname}} +.endd + +.wen @@ -40006,6 +40807,8 @@ of the proxy): .endd If &$proxy_session$& is set but &$proxy_external_address$& is empty there was a protocol error. +The variables &$sender_host_address$& and &$sender_host_port$& +will have values for the actual client system, not the proxy. Since the real connections are all coming from the proxy, and the per host connection tracking is done before Proxy Protocol is @@ -40178,11 +40981,9 @@ If a value is appended it may be: If mua_wrapper is set, the utf8_downconvert control is initially set to -1. -.new The smtp transport has an option &%utf8_downconvert%&. If set it must expand to one of the three values described above, and it overrides any previously set value. -.wen There is no explicit support for VRFY and EXPN. @@ -40272,7 +41073,9 @@ Events have names which correspond to the point in process at which they fire. The name is placed in the variable &$event_name$& and the event action expansion must check this, as it will be called for every possible event type. +.new The current list of events is: +.wen .display &`dane:fail after transport `& per connection &`msg:complete after main `& per message @@ -40286,6 +41089,7 @@ The current list of events is: &`tcp:close after transport `& per connection &`tls:cert before both `& per certificate in verification chain &`smtp:connect after transport `& per connection +&`smtp:ehlo after transport `& per connection .endd New event types may be added in future. @@ -40312,6 +41116,7 @@ with the event type: &`msg:host:defer `& error string &`tls:cert `& verification chain depth &`smtp:connect `& smtp banner +&`smtp:ehlo `& smtp ehlo response .endd The :defer events populate one extra variable: &$event_defer_errno$&.