X-Git-Url: https://git.exim.org/users/jgh/exim.git/blobdiff_plain/96eb7d2a5b86afec3b66a61a1ba8af82ab0c6d41..d22c942c4ba0a4e5ace2dfb856a43a19f8ed8b6d:/doc/doc-docbook/spec.xfpt diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index 48237e4ea..d566d9428 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 "4.92" +.set previousversion "4.93" .include ./local_params .set ACL "access control lists (ACLs)" .set I "    " .macro copyyear -2018 +2019 .endmacro . ///////////////////////////////////////////////////////////////////////////// @@ -371,11 +371,13 @@ 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 @@ -1886,11 +1888,10 @@ 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). @@ -1899,35 +1900,39 @@ 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. +If you do not want TLS support you should set +.code +DISABLE_TLS=yes +.endd +in &_Local/Makefile_&. + 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_OPENSSL=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_OPENSSL=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 @@ -1935,7 +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 @@ -2528,6 +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 @@ -2626,6 +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 @@ -2765,9 +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, @@ -3717,6 +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 @@ -3951,6 +3963,18 @@ 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. +.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. + .vitem &%-Mmad%&&~<&'message&~id'&>&~<&'message&~id'&>&~... .oindex "&%-Mmad%&" .cindex "delivery" "cancelling all" @@ -4161,6 +4185,7 @@ forces queueing. .vitem &%-odqs%& .oindex "&%-odqs%&" .cindex "SMTP" "delaying delivery" +.cindex "first pass routing" This option is a hybrid between &%-odb%&/&%-odi%& and &%-odq%&. However, like &%-odb%& and &%-odi%&, this option has no effect if &%queue_only_override%& is false and one of the queueing options in the @@ -4359,6 +4384,17 @@ written. When &%-oX%& is used with &%-bd%&, or when &%-q%& with a time is used without &%-bd%&, this is the only way of causing Exim to write a pid file, because in those cases, the normal pid file is not used. +.new +.vitem &%-oPX%& +.oindex "&%-oPX%&" +.cindex "pid (process id)" "of daemon" +.cindex "daemon" "process id (pid)" +This option is not intended for general use. +The daemon uses it when terminating due to a SIGTEM, possibly in +combination with &%-oP%&&~<&'path'&>. +It causes the pid file to be removed. +.wen + .vitem &%-or%&&~<&'time'&> .oindex "&%-or%&" .cindex "timeout" "for non-SMTP input" @@ -4468,6 +4504,7 @@ appear in the correct order. Each flag is described in a separate item below. .cindex "queue" "double scanning" .cindex "queue" "routing" .cindex "routing" "whole queue before delivery" +.cindex "first pass routing" An option starting with &%-qq%& requests a two-stage queue run. In the first stage, the queue is scanned as if the &%queue_smtp_domains%& option matched every domain. Addresses are routed, local deliveries happen, but no remote @@ -6251,10 +6288,6 @@ 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 = * -.endif .ifdef _HAVE_PRDR hosts_try_prdr = * .endif @@ -6262,9 +6295,7 @@ remote_smtp: 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; -see section &<>& for more details. +with over-long lines. The &%hosts_try_prdr%& option enables an efficiency SMTP option. It is negotiated between client and server and not expected to cause problems @@ -6333,7 +6364,7 @@ All other options are defaulted. .code local_delivery: driver = appendfile - file = /var/mail/$local_part + file = /var/mail/$local_part_verified delivery_date_add envelope_to_add return_path_add @@ -6341,7 +6372,17 @@ local_delivery: # mode = 0660 .endd This &(appendfile)& transport is used for local delivery to user mailboxes in -traditional BSD mailbox format. By default it runs under the uid and gid of the +traditional BSD mailbox format. + +.new +We prefer to avoid using &$local_part$& directly to define the mailbox filename, +as it is provided by a potential bad actor. +Instead we use &$local_part_verified$&, +the result of looking up &$local_part$& in the user database +(done by using &%check_local_user%& in the the router). +.wen + +By default &(appendfile)& runs under the uid and gid of the local user, which requires the sticky bit to be set on the &_/var/mail_& directory. Some systems use the alternative approach of running mail deliveries under a particular group instead of using the sticky bit. The commented options @@ -6655,11 +6696,10 @@ 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 @@ -6744,13 +6784,10 @@ lookup types support only literal keys. 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 @@ -6767,7 +6804,6 @@ 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" @@ -7321,7 +7357,7 @@ 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. @@ -8266,6 +8302,19 @@ domainlist dom2 = !a.b : *.b where &'x.y'& does not match. It's best to avoid negation altogether in referenced lists if you can. +.new +.cindex "hiding named list values" +.cindex "named lists" "hiding value of" +Some named list definitions may contain sensitive data, for example, passwords for +accessing databases. To stop non-admin users from using the &%-bP%& command +line option to read these values, you can precede the definition with the +word &"hide"&. For example: +.code +hide domainlist filter_for_domains = ldap;PASS=secret ldap::/// ... +.endd +.wen + + Named lists may have a performance advantage. When Exim is routing an address or checking an incoming message, it caches the result of tests on named lists. So, if you have a setting such as @@ -8687,11 +8736,9 @@ 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. -.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)&. @@ -9211,7 +9258,11 @@ 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, +.cindex "tainted data" expansion +.cindex expansion "tainted data" +and expansion of data deriving from the sender (&"tainted data"&) +is not permitted. @@ -9361,7 +9412,7 @@ 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. @@ -9458,9 +9509,13 @@ set in &_Local/Makefile_&. Once loaded, Exim remembers the dynamically loaded object so that it doesn't reload the same object file in the same Exim process (but of course Exim does start new processes frequently). -There may be from zero to eight arguments to the function. When compiling -a local function that is to be called in this way, &_local_scan.h_& should be -included. The Exim variables and functions that are defined by that API +There may be from zero to eight arguments to the function. + +When compiling +a local function that is to be called in this way, +first &_DLFUNC_IMPL_& should be defined, +and second &_local_scan.h_& should be included. +The Exim variables and functions that are defined by that API are also available for dynamically loaded functions. The function itself must have the following type: .code @@ -9569,10 +9624,8 @@ 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. @@ -9623,10 +9676,8 @@ 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 .vitem &*${filter{*&<&'string'&>&*}{*&<&'condition'&>&*}}*& @@ -9645,7 +9696,7 @@ 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 &*${hash{*&<&'string1'&>&*}{*&<&'string2'&>&*}{*&<&'string3'&>&*}}*& @@ -9683,7 +9734,7 @@ letters appear. For example: "&*$bheader_*&<&'header&~name'&>&*:*&&~or&~&&& &*$bh_*&<&'header&~name'&>&*:*&" &&& "&*$lheader_*&<&'header&~name'&>&*:*&&~or&~&&& - &*$lh_*&<&'header&~name'&>&*:*&" + &*$lh_*&<&'header&~name'&>&*:*&" &&& "&*$rheader_*&<&'header&~name'&>&*:*&&~or&~&&& &*$rh_*&<&'header&~name'&>&*:*&" .cindex "expansion" "header insertion" @@ -9789,6 +9840,12 @@ newline at the very end. For the &%header%& and &%bheader%& expansion, for those headers that contain lists of addresses, a comma is also inserted at the junctions between headers. This does not happen for the &%rheader%& expansion. +.new +.cindex "tainted data" +When the headers are from an incoming message, +the result of expanding any of these variables is tainted. +.wen + .vitem &*${hmac{*&<&'hashname'&>&*}{*&<&'secret'&>&*}{*&<&'string'&>&*}}*& .cindex "expansion" "hmac hashing" @@ -9996,8 +10053,8 @@ 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 &*${nhash{*&<&'string1'&>&*}{*&<&'string2'&>&*}{*&<&'string3'&>&*}}*& .cindex "expansion" "numeric hash" @@ -10196,7 +10253,7 @@ assigned to the &$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}}} @@ -10207,7 +10264,7 @@ 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'&>&*:*& @@ -10467,9 +10524,9 @@ 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 @@ -10957,11 +11014,15 @@ 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. @@ -10969,6 +11030,13 @@ 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. +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. + .vitem &*${sha3:*&<&'string'&>&*}*& &&& &*${sha3_:*&<&'string'&>&*}*& @@ -11349,12 +11417,11 @@ 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'&>&*}*&" &&& @@ -11370,7 +11437,6 @@ 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 @@ -12050,6 +12116,13 @@ 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. +.vitem &$dmarc_domain_policy$& &&& + &$dmarc_status$& &&& + &$dmarc_status_text$& &&& + &$dmarc_used_domains$& +Results of DMARC verification. +For details see section &<>&. + .vitem &$dkim_verify_status$& Results of DKIM verification. For details see section &<>&. @@ -12150,6 +12223,13 @@ When the &%smtp_etrn_command%& option is being expanded, &$domain$& contains the complete argument of the ETRN command (see section &<>&). .endlist +.new +.cindex "tainted data" +If the origin of the data is an incoming message, +the result of expanding this variable is tainted. +See also &$domain_verified$&. +.wen + .vitem &$domain_data$& .vindex "&$domain_data$&" @@ -12277,7 +12357,7 @@ 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 &$host_lookup_failed$& @@ -12343,6 +12423,25 @@ Global address rewriting happens when a message is received, so the value of because a message may have many recipients and the system filter is called just once. +.new +.cindex "tainted data" +If the origin of the data is an incoming message, +the result of expanding this variable is tainted. + +&*Warning*&: the content of this variable is usually provided by a potential +attacker. +Consider carefully the implications of using it unvalidated as a name +for file access. +This presents issues for users' &_.forward_& and filter files. +For traditional full user accounts, use &%check_local_users%& and the +&$local_part_verified$& variable rather than this one. +For virtual users, store a suitable pathname component in the database +which is used for account name validation, and use that retrieved value +rather than this variable. +If needed, use a router &%address_data%& or &%set%& option for +the retrieved data. +.wen + .vindex "&$local_part_prefix$&" .vindex "&$local_part_suffix$&" .cindex affix variables @@ -12409,6 +12508,14 @@ When an address is being routed or delivered, and a specific suffix for the local part was recognized, it is available in this variable, having been removed from &$local_part$&. +.new +.vitem &$local_part_verified$& +.vindex "&$local_part_verified$&" +If the router generic option &%check_local_part%& has run successfully, +this variable has the user database version of &$local_part$&. +Such values are not tainted and hence usable for building file names. +.wen + .vitem &$local_scan_data$& .vindex "&$local_scan_data$&" This variable contains the text returned by the &[local_scan()]& function when @@ -12743,6 +12850,14 @@ 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. +.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. + .vitem &$rcpt_count$& .vindex "&$rcpt_count$&" When a message is being received by SMTP, this variable contains the number of @@ -13305,6 +13420,7 @@ 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. +The macro "_TLS_BAD_MULTICERT_IN_OURCERT" will be defined for those versions. .vitem &$tls_in_peercert$& .vindex "&$tls_in_peercert$&" @@ -13361,11 +13477,9 @@ 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 "&$tls_out_cipher$&" @@ -13375,11 +13489,9 @@ 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 &$tls_out_dane$& @@ -13454,6 +13566,17 @@ the transport. .vindex &$tls_out_tlsa_usage$& Bitfield of TLSA record types found. See section &<>&. +.vitem &$tls_in_ver$& +.vindex "&$tls_in_ver$&" +When a message is received from a remote host over an encrypted SMTP connection +this variable is set to the protocol version, eg &'TLS1.2'&. + +.vitem &$tls_out_ver$& +.vindex "&$tls_out_ver$&" +When a message is being delivered to a remote host over an encrypted SMTP connection +this variable is set to the protocol version. + + .vitem &$tod_bsdinbox$& .vindex "&$tod_bsdinbox$&" The time of day and the date, in the format required for BSD-style mailbox @@ -14310,7 +14433,9 @@ 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" @@ -14355,6 +14480,7 @@ 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" @@ -14595,8 +14721,10 @@ received. See chapter &<>& for further details. .option add_environment main "string list" empty .cindex "environment" "set values" -This option allows to set individual environment variables that the -currently linked libraries and programs in child processes use. +This option adds individual environment variables that the +currently linked libraries and programs in child processes may use. +Each list element should be of the form &"name=value"&. + See &<>& for the environment of &(pipe)& transports. .option admin_groups main "string list&!!" unset @@ -14640,13 +14768,18 @@ 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. + +If Exim is built with internationalization support +and the SMTPUTF8 ESMTP option is in use (see chapter &<>&) +this option can be left as default. +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 @@ -15054,6 +15187,32 @@ 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" +.cindex DKIM "selecting signature algorithms" +This option gives a list of hash types which are acceptable in signatures, +.wen +and an order of processing. +Signatures with algorithms not in the list will be ignored. + +Acceptable values include: +.code +sha1 +sha256 +sha512 +.endd + +Note that the acceptance of sha1 violates RFC 8301. + +.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. + .option dkim_verify_signers main "domain list&!!" $dkim_signers .cindex DKIM "controlling calls to the ACL" This option gives a list of DKIM domains for which the DKIM ACL is run. @@ -15145,6 +15304,9 @@ domain matches this list. This is a fudge to help with name servers that give big delays or otherwise do not work for the AAAA record type. In due course, when the world's name servers have all been upgraded, there should be no need for this option. +Note that all lookups, including those done for verification, are affected; +this will result in verify failure for IPv6 connections or ones using names +only valid for IPv6 addresses. .option dns_retrans main time 0s @@ -15351,8 +15513,8 @@ used. See chapter &<>& for a discussion of security issues. .cindex "Exim version" .cindex customizing "version number" .cindex "version number of Exim" override -This option allows to override the &$version_number$&/&$exim_version$& Exim reports in -various places. Use with care, this may fool stupid security scanners. +This option overrides the &$version_number$&/&$exim_version$& that Exim reports in +various places. Use with care; this may fool stupid security scanners. .option extra_local_interfaces main "string list" unset @@ -15874,6 +16036,7 @@ 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 @@ -15974,6 +16137,8 @@ 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. +A path must start with a slash. +To send to syslog, use the word &"syslog"&. 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 @@ -16180,7 +16345,7 @@ harm. This option overrides the &%pipe_as_creator%& option of the &(pipe)& transport driver. -.option openssl_options main "string list" "+no_sslv2 +no_sslv3 +single_dh_use +no_ticket" +.option openssl_options main "string list" "+no_sslv2 +no_sslv3 +single_dh_use +no_ticket +no_renegotiation" .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, @@ -16321,9 +16486,9 @@ interpreter. See chapter &<>& for details of its use. This option is available only when Exim is built with an embedded Perl interpreter. See chapter &<>& for details of its use. -.option perl_startup main boolean false +.option perl_taintmode main boolean false .cindex "Perl" -This Option enables the taint mode of the embedded Perl interpreter. +This option enables the taint mode of the embedded Perl interpreter. .option pgsql_servers main "string list" unset @@ -16360,6 +16525,19 @@ 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%&). +.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. + .option prdr_enable main boolean false .cindex "PRDR" "enabling on server" @@ -16590,6 +16768,7 @@ an expansion depending on the &$queue_name$& variable. .option queue_smtp_domains main "domain list&!!" unset .cindex "queueing incoming messages" .cindex "message" "queueing remote deliveries" +.cindex "first pass routing" When this option is set, a delivery process is started whenever a message is received, routing is performed, and local deliveries take place. However, if any SMTP deliveries are required for domains that match @@ -16621,7 +16800,6 @@ 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. -.new The default setting is: .code @@ -16632,6 +16810,7 @@ received_header_text = Received: \ ${if def:sender_helo_name {(helo=$sender_helo_name)\n\t}}}}\ by $primary_hostname \ ${if def:received_protocol {with $received_protocol }}\ + ${if def:tls_ver { ($tls_ver)}}\ ${if def:tls_in_cipher_std { tls $tls_in_cipher_std\n\t}}\ (Exim $version_number)\n\t\ ${if def:sender_address \ @@ -16639,7 +16818,6 @@ received_header_text = Received: \ id $message_exim_id\ ${if def:received_for {\n\tfor $received_for}} .endd -.wen The reference to the TLS cipher is omitted when Exim is built without TLS support. The use of conditional expansions ensures that this works for both @@ -16818,12 +16996,6 @@ it qualifies them only if the message came from a host that matches &%sender_unqualified_hosts%&, or if the message was submitted locally (not using TCP/IP), and the &%-bnq%& option was not set. -.option set_environment main "string list" empty -.cindex "environment" -This option allows to set individual environment variables that the -currently linked libraries and programs in child processes use. The -default list is empty, - .option slow_lookup_log main integer 0 .cindex "logging" "slow lookups" @@ -17564,8 +17736,8 @@ is not required the &%tls_advertise_hosts%& option should be set empty. .cindex "TLS" "server certificate; location of" .cindex "certificate" "server, location of" The value of this option is expanded, and must then be a list of absolute paths to -files which contains the server's certificates. Commonly only one file is -needed. +files which contain the server's certificates (in PEM format). +Commonly only one file is needed. The server's private key is also assumed to be in this file if &%tls_privatekey%& is unset. See chapter &<>& for further details. @@ -17581,9 +17753,7 @@ separator in the usual way (&<>&) to avoid confusion under IP &*Note*&: Under versions of OpenSSL preceding 1.1.1, when a list of more than one file is used, the &$tls_in_ourcert$& variable is unreliable. - -&*Note*&: OCSP stapling is not usable under OpenSSL -when a list of more than one file is used. +The macro "_TLS_BAD_MULTICERT_IN_OURCERT" will be defined for those versions. If the option contains &$tls_out_sni$& and Exim is built against OpenSSL, then if the OpenSSL build supports TLS extensions and the TLS client sends the @@ -17634,7 +17804,12 @@ 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 +This option is ignored for GnuTLS version 3.6.0 and later. +The library manages parameter negotiation internally. + +&*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. @@ -17729,11 +17904,29 @@ 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). +The macro "_HAVE_TLS_OCSP" will be defined for those versions. -For GnuTLS 3.5.6 or later the expanded value of this option can be a list +For OpenSSL 1.1.0 or later, and +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. - +The macro "_HAVE_TLS_OCSP_LIST" will be defined for those versions. + +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. .option tls_on_connect_ports main "string list" unset .cindex SSMTP @@ -17891,6 +18084,7 @@ 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 @@ -18041,6 +18235,8 @@ file = ${extract{mailbox}{$address_data}} This makes the configuration file less messy, and also reduces the number of lookups (though Exim does cache lookups). +See also the &%set%& option below. + .vindex "&$sender_address_data$&" .vindex "&$address_data$&" The &%address_data%& facility is also useful as a means of passing information @@ -18246,7 +18442,7 @@ 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" @@ -18293,6 +18489,7 @@ 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 @@ -18821,11 +19018,22 @@ 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%& +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%& 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. @@ -18954,6 +19162,30 @@ SMTP VRFY command is enabled, it must be used after MAIL if the sender address matters. +.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. +Variable 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. + + .option translate_ip_address routers string&!! unset .cindex "IP address" "translating" .cindex "packet radio" @@ -20362,6 +20594,19 @@ is not the case when the file contains syntactically valid items that happen to yield empty addresses, for example, items containing only RFC 2822 address comments. +.new +.cindex "tainted data" "in filenames" +.cindex redirect "tainted data" +Tainted data may not be used for a filename. + +&*Warning*&: It is unwise to use &$local_part$& or &$domain$& +directly for redirection, +as they are provided by a potential attacker. +In the examples above, &$local_part$& is used for looking up data held locally +on the system, and not used directly (the second example derives &$home$& via +the passsword file or database, using &$local_part$&). +.wen + .section "Forward files and address verification" "SECID125" @@ -20587,6 +20832,11 @@ It must be given as .code list1: :include:/opt/lists/list1 .endd +.new +.cindex "tainted data" "in filenames" +.cindex redirect "tainted data" +Tainted data may not be used for a filename. +.wen .next .cindex "address redirection" "to black hole" .cindex "delivery" "discard" @@ -21739,6 +21989,7 @@ 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 @@ -22145,6 +22396,14 @@ If &%file%& or &%directory%& is set for a delivery from a redirection, it is used to determine the file or directory name for the delivery. Normally, the contents of &$address_file$& are used in some way in the string expansion. .endlist +.new +.cindex "tainted data" "in filenames" +.cindex appendfile "tainted data" +Tainted data may not be used for a file or directory name. +This means that, for instance, &$local_part$& cannot be used directly +as a component of a path. It can however be used as the key for a lookup +which returns a path (or component). +.wen .cindex "Sieve filter" "configuring &(appendfile)&" @@ -22733,6 +22992,13 @@ sometimes add other information onto the ends of message filenames. Section &<>& contains further information. +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. + .option quota_warn_message appendfile string&!! "see below" See below for the use of this option. If it is not set when @@ -22785,6 +23051,7 @@ 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 @@ -23574,6 +23841,12 @@ directories are also controllable. See chapter &<>& for details of the local delivery environment and chapter &<>& for a discussion of local delivery batching. +.new +.cindex "tainted data" "in pipe command" +.cindex pipe "tainted data" +Tainted data may not be used for the command name. +.wen + .section "Concurrent delivery" "SECID140" If two messages arrive at almost the same time, and both are routed to a pipe @@ -23669,7 +23942,7 @@ 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 @@ -24326,15 +24599,23 @@ 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 @@ -24376,14 +24657,15 @@ 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. @@ -24393,9 +24675,9 @@ 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. @@ -24540,6 +24822,30 @@ 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. +.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. + .option hosts_avoid_tls smtp "host list&!!" unset .cindex "TLS" "avoiding for certain hosts" @@ -24579,7 +24885,6 @@ 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. -.new .option hosts_noproxy_tls smtp "host list&!!" unset .cindex "TLS" "passing connection" .cindex "multiple SMTP deliveries" @@ -24587,7 +24892,6 @@ explanation of when this might be needed. 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 @@ -24650,7 +24954,8 @@ 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 &<>&. @@ -24681,19 +24986,22 @@ unauthenticated. See also &%hosts_require_auth%&, and chapter .cindex "RFC 3030" "CHUNKING" This option provides a list of servers to which, provided they announce CHUNKING support, Exim will attempt to use BDAT commands rather than DATA. +.new +Unless DKIM signing is being done, +.wen 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" @@ -25256,6 +25564,7 @@ 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" @@ -26236,10 +26545,8 @@ 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. -.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 sixth provides direct access to Heimdal GSSAPI, geared for Kerberos, but @@ -26528,7 +26835,7 @@ no successful authentication. .cindex authentication "expansion item" Successful authentication sets up information used by the -&$authresults$& expansion item. +&%authresults%& expansion item. @@ -26664,7 +26971,19 @@ security risk; you are strongly advised to insist on the use of SMTP encryption use unencrypted plain text, you should not use the same passwords for SMTP connections as you do for login accounts. -.section "Plaintext options" "SECID171" +.section "Avoiding cleartext use" "SECTplain_TLS" +The following generic option settings will disable &(plaintext)& authenticators when +TLS is not being used: +.code + server_advertise_condition = ${if def:tls_in_cipher } + client_condition = ${if def:tls_out_cipher} +.endd + +&*Note*&: a plaintext SMTP AUTH done inside TLS is not vulnerable to casual snooping, +but is still vulnerable to a Man In The Middle attack unless certificates +(including their names) have been properly verified. + +.section "Plaintext server options" "SECID171" .cindex "options" "&(plaintext)& authenticator (server)" When configured as a server, &(plaintext)& uses the following options: @@ -26672,7 +26991,7 @@ When configured as a server, &(plaintext)& uses the following options: This is actually a global authentication option, but it must be set in order to configure the &(plaintext)& driver as a server. Its use is described below. -.option server_prompts plaintext string&!! unset +.option server_prompts plaintext "string list&!!" unset The contents of this option, after expansion, must be a colon-separated list of prompt strings. If expansion fails, a temporary authentication rejection is given. @@ -27142,7 +27461,7 @@ but it is present in many binary distributions. .scindex IIDdcotauth1 "&(dovecot)& authenticator" .scindex IIDdcotauth2 "authenticators" "&(dovecot)&" This authenticator is an interface to the authentication facility of the -Dovecot POP/IMAP server, which can support a number of authentication methods. +Dovecot 2 POP/IMAP server, which can support a number of authentication methods. Note that Dovecot must be configured to use auth-client not auth-userdb. If you are using Dovecot to authenticate POP/IMAP clients, it might be helpful to use the same mechanisms for SMTP authentication. This is a server @@ -27173,6 +27492,29 @@ option is passed in the Dovecot authentication command. If, for a TLS connection, a client certificate has been verified, the &"valid-client-cert"& option is passed. When authentication succeeds, the identity of the user who authenticated is placed in &$auth1$&. + +.new +The Dovecot configuration to match the above wil look +something like: +.code +conf.d/10-master.conf :- + +service auth { +... +#SASL + unix_listener auth-client { + mode = 0660 + user = mail + } +... +} + +conf.d/10-auth.conf :- + +auth_mechanisms = plain login ntlm +.endd +.wen + .ecindex IIDdcotauth1 .ecindex IIDdcotauth2 @@ -27191,19 +27533,58 @@ who authenticated is placed in &$auth1$&. .cindex "authentication" "DIGEST-MD5" .cindex "authentication" "CRAM-MD5" .cindex "authentication" "SCRAM-SHA-1" -The &(gsasl)& authenticator provides server integration for the GNU SASL +.cindex "authentication" "SCRAM-SHA-1-PLUS" +.cindex "authentication" "SCRAM-SHA-256" +.cindex "authentication" "SCRAM-SHA-256-PLUS" +The &(gsasl)& authenticator provides integration for the GNU SASL library and the mechanisms it provides. This is new as of the 4.80 release and there are a few areas where the library does not let Exim smoothly scale to handle future authentication mechanisms, so no guarantee can be made that any particular new authentication mechanism will be supported without code changes in Exim. -Exim's &(gsasl)& authenticator does not have client-side support at this -time; only the server-side support is implemented. Patches welcome. +.new +The library is expected to add support in an upcoming +realease for the SCRAM-SHA-256 method. +The macro _HAVE_AUTH_GSASL_SCRAM_SHA_256 will be defined +when this happens. + + +.option client_authz gsasl string&!! unset +This option can be used to supply an &'authorization id'& +which is different to the &'authentication_id'& provided +by &%client_username%& option. +If unset or (after expansion) empty it is not used, +which is the common case. + +.option client_channelbinding gsasl boolean false +See &%server_channelbinding%& below. + +.option client_password gsasl string&!! unset +This option is exapanded before use, and should result in +the password to be used, in clear. + +.option client_username gsasl string&!! unset +This option is exapanded before use, and should result in +the account name to be used. +.wen + +.new +.option client_spassword gsasl string&!! unset +If a SCRAM mechanism is being used and this option is set +it is used in preference to &%client_password%&. +The value after expansion should be +a 40 (for SHA-1) or 64 (for SHA-256) character string +with the PBKDF2-prepared password, hex-encoded. +Note that this value will depend on the salt and iteration-count +supplied by the server. +.wen + .option server_channelbinding gsasl boolean false -Do not set this true without consulting a cryptographic engineer. +Do not set this true and rely on the properties +without consulting a cryptographic engineer. Some authentication mechanisms are able to use external context at both ends of the session to bind the authentication to that context, and fail the @@ -27215,15 +27596,18 @@ This should have meant that certificate identity and verification becomes a non-issue, as a man-in-the-middle attack will cause the correct client and server to see different identifiers and authentication will fail. -This is currently only supported when using the GnuTLS library. This is +.new +This is only usable by mechanisms which support "channel binding"; at time of writing, that's the SCRAM family. +When using this feature the "-PLUS" variants of the method names need to be used. +.wen This defaults off to ensure smooth upgrade across Exim releases, in case this option causes some clients to start failing. Some future release of Exim might have switched the default to be true. -However, Channel Binding in TLS has proven to be broken in current versions. +However, Channel Binding in TLS has proven to be vulnerable in current versions. Do not plan to rely upon this feature for security, ever, without consulting with a subject matter expert (a cryptographic engineer). @@ -27271,16 +27655,60 @@ This specifies the SASL realm that the server claims to be in. Some mechanisms will use this data. -.option server_scram_iter gsasl string&!! unset +.option server_scram_iter gsasl string&!! 4096 This option provides data for the SCRAM family of mechanisms. -&$auth1$& is not available at evaluation time. -(This may change, as we receive feedback on use) - +.new +The &$auth1$&, &$auth2$& and &$auth3$& variables are available +when this option is expanded. + +The result of expansion should be a decimal number, +and represents both a lower-bound on the security, and +a compute cost factor imposed on the client +(if it does not cache results, or the server changes +either the iteration count or the salt). +A minimum value of 4096 is required by the standards +for all current SCRAM mechanism variants. +.wen .option server_scram_salt gsasl string&!! unset This option provides data for the SCRAM family of mechanisms. -&$auth1$& is not available at evaluation time. -(This may change, as we receive feedback on use) +.new +The &$auth1$&, &$auth2$& and &$auth3$& variables are available +when this option is expanded. +The value should be a base64-encoded string, +of random data typically 4-to-16 bytes long. +If unset or empty after expansion the library will provides a value for the +protocol conversation. +.wen + + +.new +.option server_key gsasl string&!! unset +.option server_skey gsasl string&!! unset +These options can be used for the SCRAM family of mechanisms +to provide stored information related to a password, +the storage of which is preferable to plaintext. + +&%server_key%& is the value defined in the SCRAM standards as ServerKey; +&%server_skey%& is StoredKey. + +They are only available for version 1.9.0 (or later) of the gsasl library. +When this is so, the macros +_OPT_AUTHENTICATOR_GSASL_SERVER_KEY +and _HAVE_AUTH_GSASL_SCRAM_S_KEY +will be defined. + +The &$authN$& variables are available when these options are expanded. + +If set, the results of expansion should for each +should be a 28 (for SHA-1) or 44 (for SHA-256) character string +of base64-coded data, and will be used in preference to the +&%server_password%& option. +If unset or not of the right length, &%server_password%& will be used. + +The libgsasl library release includes a utility &'gsasl'& which can be used +to generate these values. +.wen .option server_service gsasl string &`smtp`& @@ -27588,11 +28016,10 @@ 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, +&*Note*&: 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" @@ -27805,16 +28232,19 @@ There is also a &%-tls-on-connect%& command line option. This overrides .section "OpenSSL vs GnuTLS" "SECTopenvsgnu" .cindex "TLS" "OpenSSL &'vs'& GnuTLS" -The first TLS support in Exim was implemented using OpenSSL. Support for GnuTLS -followed later, when the first versions of GnuTLS were released. To build Exim -to use GnuTLS, you need to set +TLS is supported in Exim using either the OpenSSL or GnuTLS library. +To build Exim to use OpenSSL you need to set .code -USE_GNUTLS=yes +USE_OPENSSL=yes .endd -in Local/Makefile, in addition to +in Local/Makefile. + +To build Exim to use GnuTLS, you need to set .code -SUPPORT_TLS=yes +USE_GNUTLS=yes .endd +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. @@ -28372,6 +28802,11 @@ 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. +&*Note*&: Do not use a certificate which has the OCSP-must-staple extension, +for client use (they are usable for server use). +As the TLS protocol has no means for the client to staple before TLS 1.3 it will result +in failed connections. + If the &%tls_verify_certificates%& option is set on the &(smtp)& transport, it specifies a collection of expected server certificates. These may be @@ -28495,7 +28930,7 @@ 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. @@ -28690,7 +29125,12 @@ 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); @@ -28731,19 +29171,29 @@ 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. -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). @@ -28777,7 +29227,9 @@ 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. @@ -28807,7 +29259,8 @@ 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". @@ -30126,6 +30579,13 @@ This control turns off DKIM verification processing entirely. For details on the operation and configuration of DKIM, see section &<>&. +.vitem &*control&~=&~dmarc_disable_verify*& +.cindex "disable DMARC verify" +.cindex "DMARC" "disable verify" +This control turns off DMARC verification processing entirely. For details on +the operation and configuration of DMARC, see section &<>&. + + .vitem &*control&~=&~dscp/*&<&'value'&> .cindex "&ACL;" "setting DSCP value" .cindex "DSCP" "inbound" @@ -30260,16 +30720,32 @@ response to an EHLO command. Therefore, it should normally appear in an ACL controlled by &%acl_smtp_connect%& or &%acl_smtp_helo%&. See also &%pipelining_advertise_hosts%&. -.vitem &*control&~=&~queue_only*& +.new +.vitem &*control&~=&~queue/*&<&'options'&>* &&& + &*control&~=&~queue_only*& +.oindex "&%queue%&" .oindex "&%queue_only%&" .cindex "queueing incoming messages" +.cindex queueing "forcing in ACL" +.cindex "first pass routing" This control is permitted only for the MAIL, RCPT, DATA, and non-SMTP ACLs, in other words, only when a message is being received. If the message is accepted, it is placed on Exim's queue and left there for delivery by a subsequent queue -runner. No immediate delivery process is started. In other words, it has the -effect as the &%queue_only%& global option. However, the control applies only -to the current message, not to any subsequent ones that may be received in the -same SMTP connection. +runner. +If used with no options set, +no immediate delivery process is started. In other words, it has the +effect as the &%queue_only%& global option or &'-odq'& command-line option. + +If the &'first_pass_route'& option is given then +the behaviour is like the command-line &'-oqds'& option; +a delivery process is started which stops short of making +any SMTP delivery. The benefit is that the hints database will be updated for +the message being waiting for a specific host, and a later queue run will be +able to send all such messages on a single connection. + +The control only applies to the current message, not to any subsequent ones that + may be received in the same SMTP connection. +.wen .vitem &*control&~=&~submission/*&<&'options'&> .cindex "message" "submission" @@ -30690,7 +31166,9 @@ 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'&> @@ -30851,7 +31329,7 @@ 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. @@ -30867,10 +31345,8 @@ 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. @@ -32478,6 +32954,13 @@ 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. +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%& + A timeout of 2 minutes is applied to a scanner call (by default); if it expires then a defer action is taken. @@ -33386,7 +33869,12 @@ directory, so you might set HAVE_LOCAL_SCAN=yes LOCAL_SCAN_SOURCE=Local/local_scan.c .endd -for example. The function must be called &[local_scan()]&. It is called by +for example. The function must be called &[local_scan()]&; +.new +the source file(s) for it should first #define LOCAL_SCAN +and then #include "local_scan.h". +.wen +It is called by Exim after it has received a message, when the success return code is about to be sent. This is after all the ACLs have been run. The return code from your function controls whether the message is actually accepted or not. There is a @@ -34016,8 +34504,8 @@ with translation. This function is used in conjunction with &'smtp_printf()'&, as described below. -.vitem &*void&~smtp_printf(char&~*,&~...)*& -The arguments of this function are like &[printf()]&; it writes to the SMTP +.vitem &*void&~smtp_printf(char&~*,BOOL,&~...)*& +The arguments of this function are almost like &[printf()]&; it writes to the SMTP output stream. You should use this function only when there is an SMTP output stream, that is, when the incoming message is being received via interactive SMTP. This is the case when &%smtp_input%& is TRUE and &%smtp_batched_input%& @@ -34029,6 +34517,15 @@ is involved. If an SMTP TLS connection is established, &'smtp_printf()'& uses the TLS output function, so it can be used for all forms of SMTP connection. +The second argument is used to request that the data be buffered +(when TRUE) or flushed (along with any previously buffered, when FALSE). +This is advisory only, but likely to save on system-calls and packets +sent when a sequence of calls to the function are made. + +The argument was added in Exim version 4.90 - changing the API/ABI. +Nobody noticed until 4.93 was imminent, at which point the +ABI version number was incremented. + Strings that are written by &'smtp_printf()'& from within &[local_scan()]& must start with an appropriate response code: 550 if you are going to return LOCAL_SCAN_REJECT, 451 if you are going to return @@ -34046,7 +34543,9 @@ the data returned via the &%return_text%& argument. The added value of using multiple output lines. The &'smtp_printf()'& function does not return any error indication, because it -does not automatically flush pending output, and therefore does not test +does not +guarantee a flush of +pending output, and therefore does not test the state of the stream. (In the main code of Exim, flushing and error detection is done when Exim is ready for the next SMTP input command.) If you want to flush the output and check for an error (for example, the @@ -34054,12 +34553,18 @@ dropping of a TCP/IP connection), you can call &'smtp_fflush()'&, which has no arguments. It flushes the output stream, and returns a non-zero value if there is an error. -.vitem &*void&~*store_get(int)*& +.new +.vitem &*void&~*store_get(int,BOOL)*& This function accesses Exim's internal store (memory) manager. It gets a new -chunk of memory whose size is given by the argument. Exim bombs out if it ever +chunk of memory whose size is given by the first argument. +The second argument should be given as TRUE if the memory will be used for +data possibly coming from an attacker (eg. the message content), +FALSE if it is locally-sourced. +Exim bombs out if it ever runs out of memory. See the next section for a discussion of memory handling. +.wen -.vitem &*void&~*store_get_perm(int)*& +.vitem &*void&~*store_get_perm(int,BOOL)*& This function is like &'store_get()'&, but it always gets memory from the permanent pool. See the next section for a discussion of memory handling. @@ -34359,6 +34864,7 @@ 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 @@ -34592,6 +35098,7 @@ 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 @@ -36040,6 +36547,7 @@ 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 @@ -36370,6 +36878,7 @@ delivered immediately. .cindex "SMTP" "passed connection" .cindex "SMTP" "multiple deliveries" .cindex "multiple SMTP deliveries" +.cindex "first pass routing" Mail waiting to be sent from an intermittently connected host will probably not have been routed, because without a connection DNS lookups are not possible. This means that if a normal queue run is done at connection time, @@ -37027,7 +37536,7 @@ the following table: &`DKIM`& domain verified in incoming message &`DN `& distinguished name from peer certificate &`DS `& DNSSEC secured lookups -&`DT `& on &`=>`& lines: time taken for a delivery +&`DT `& on &`=>`&, &'=='& and &'**'& lines: time taken for, or to attempt, a delivery &`F `& sender address (on delivery lines) &`H `& host name and IP address &`I `& local interface used @@ -37125,7 +37634,7 @@ selection marked by asterisks: &` arguments `& command line arguments &`*connection_reject `& connection rejections &`*delay_delivery `& immediate delivery delayed -&` deliver_time `& time taken to perform delivery +&` deliver_time `& time taken to attempt delivery &` delivery_size `& add &`S=`&&'nnn'& to => lines &`*dkim `& DKIM verified domain on <= lines &` dkim_verbose `& separate full DKIM verification result line, per signature @@ -37323,7 +37832,6 @@ 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 @@ -37331,7 +37839,6 @@ appended to the seconds value. 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" @@ -37367,6 +37874,13 @@ 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. + +.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. + .next .cindex "log" "queue run" .cindex "queue runner" "logging" @@ -37723,10 +38237,8 @@ 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: @@ -39414,6 +39926,9 @@ was received from the client, this records the Distinguished Name from that certificate. .endlist +Any of the above may have an extra hyphen prepended, to indicate the the +corresponding data is untrusted. + 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%& @@ -39522,11 +40037,11 @@ 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 @@ -39602,9 +40117,7 @@ These options take (expandable) strings as arguments. The domain(s) you want to sign with. After expansion, this can be a list. 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, @@ -39659,9 +40172,7 @@ Signers MUST use RSA keys of at least 1024 bits for all keys. Signers SHOULD use RSA keys of at least 2048 bits. .endd -.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) @@ -39681,12 +40192,10 @@ 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 -.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: @@ -39760,15 +40269,24 @@ RFC 6376 lists these tags as RECOMMENDED. 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. +.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. + .cindex authentication "expansion item" Performing verification sets up information used by the -&$authresults$& expansion item. +&%authresults%& expansion item. -The results of that verification are then made available to the +For most purposes the default option settings suffice and the remainder +of this section can be ignored. + +The results of verification are made available to the &%acl_smtp_dkim%& ACL, which can examine and modify them. -By default, this ACL is called once for each -syntactically(!) correct signature in the incoming message. 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). @@ -39779,11 +40297,11 @@ 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 @@ -39809,19 +40327,17 @@ 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): @@ -39915,8 +40431,10 @@ 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, +or have set the main option &%dkim_verify_hashes%& to exclude +processing of such signatures. .vitem &%$dkim_canon_body%& The body canonicalization method. One of 'relaxed' or 'simple'. @@ -40031,8 +40549,12 @@ for more information of what they mean. SPF is a mechanism whereby a domain may assert which IP addresses may transmit messages with its domain in the envelope from, documented by RFC 7208. -For more information on SPF see &url(http://www.openspf.org). -. --- 2018-09-07: still not https +For more information on SPF see &url(http://www.open-spf.org), a static copy of +the &url(http://openspf.org). +. --- 2019-10-28: still not https, open-spf.org is told to be a +. --- web-archive copy of the now dead openspf.org site +. --- See https://www.mail-archive.com/mailop@mailop.org/msg08019.html for a +. --- discussion. Messages sent by a system not authorised will fail checking of such assertions. This includes retransmissions done by traditional forwarders. @@ -40046,7 +40568,7 @@ publishing certain DNS records is all that is required. For verification, an ACL condition and an expansion lookup are provided. .cindex authentication "expansion item" Performing verification sets up information used by the -&$authresults$& expansion item. +&%authresults%& expansion item. .cindex SPF "ACL condition" @@ -40095,7 +40617,7 @@ 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}};\ @@ -40148,9 +40670,9 @@ 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: @@ -40183,7 +40705,9 @@ 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 +(v4 or v6) +as the database: .code ${lookup {username@domain} spf {ip.ip.ip.ip}} @@ -40191,7 +40715,243 @@ address as the key and an IP address as the database: The lookup will return the same result strings as can appear in &$spf_result$& (pass,fail,softfail,neutral,none,err_perm,err_temp). -Currently, only IPv4 addresses are supported. + + + + + +.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 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/public_suffix_list.dat). +See also the util/renew-opendmarc-tlds.sh script. +.new +The default for the option is unset. +If not set, DMARC processing is disabled. +.wen + + +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 an ACL control modifier: +.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 is 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 exim 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: + +.vlist +.vitem &$dmarc_status$& +.vindex &$dmarc_status$& +.cindex DMARC result +A one word status indicating what the DMARC library +thinks of the email. It is a combination of the results of +DMARC record lookup and the SPF/DKIM/DMARC processing results +(if a DMARC record was found). The actual policy declared +in the DMARC record is in a separate expansion variable. + +.vitem &$dmarc_status_text$& +.vindex &$dmarc_status_text$& +Slightly longer, human readable status. + +.vitem &$dmarc_used_domain$& +.vindex &$dmarc_used_domain$& +The domain which DMARC used to look up the DMARC policy record. + +.vitem &$dmarc_domain_policy$& +.vindex &$dmarc_domain_policy$& +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. +.endlist + +. 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 option &%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 option &%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 {$primary_hostname}} +.endd + @@ -40520,20 +41280,24 @@ Events have names which correspond to the point in process at which they fire. The name is placed in the variable &$event_name$& and the event action expansion must check this, as it will be called for every possible event type. +.new The current list of events is: +.wen .display &`dane:fail after transport `& per connection &`msg:complete after main `& per message +&`msg:defer after transport `& per message per delivery try &`msg:delivery after transport `& per recipient &`msg:rcpt:host:defer after transport `& per recipient per host &`msg:rcpt:defer after transport `& per recipient -&`msg:host:defer after transport `& per attempt +&`msg:host:defer after transport `& per host per delivery try; host errors &`msg:fail:delivery after transport `& per recipient &`msg:fail:internal after main `& per recipient &`tcp:connect before transport `& per connection &`tcp:close after transport `& per connection &`tls:cert before both `& per certificate in verification chain &`smtp:connect after transport `& per connection +&`smtp:ehlo after transport `& per connection .endd New event types may be added in future. @@ -40552,14 +41316,16 @@ An additional variable, &$event_data$&, is filled with information varying with the event type: .display &`dane:fail `& failure reason +&`msg:defer `& error string &`msg:delivery `& smtp confirmation message &`msg:fail:internal `& failure reason &`msg:fail:delivery `& smtp error message +&`msg:host:defer `& error string &`msg:rcpt:host:defer `& error string &`msg:rcpt:defer `& error string -&`msg:host:defer `& error string &`tls:cert `& verification chain depth &`smtp:connect `& smtp banner +&`smtp:ehlo `& smtp ehlo response .endd The :defer events populate one extra variable: &$event_defer_errno$&.