X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/b2d54f831659ee95d4d4cf395f568b395e262310..5169b5fa9104c024a3d3b31b163bfa3b9ec14c9c:/doc/doc-docbook/spec.xfpt?ds=sidebyside diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index 294034a6c..ea90259f0 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -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 @@ -1906,6 +1908,7 @@ DISABLE_TLS=yes in &_Local/Makefile_&. .wen +.new If OpenSSL is installed, you should set .code USE_OPENSL=yes @@ -1914,16 +1917,17 @@ TLS_LIBS=-lssl -lcrypto in &_Local/Makefile_&. You may also need to specify the locations of the OpenSSL library and include files. For example: .code -USE_OPENSL=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 -USE_OPENSL=yes +USE_OPENSSL=yes USE_OPENSSL_PC=openssl .endd +.wen .cindex "USE_GNUTLS" If GnuTLS is installed, you should set .code @@ -3964,7 +3968,7 @@ Bounce messages are just discarded. This option can be used only by an admin user. .new -.vitem &%-MG%&&~<&'queue&~name'&&~<&'message&~id'&>&~<&'message&~id'&>&~... +.vitem &%-MG%&&~<&'queue&~name'&>&~<&'message&~id'&>&~<&'message&~id'&>&~... .oindex "&%-MG%&" .cindex queue named .cindex "named queues" @@ -6284,9 +6288,7 @@ 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 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 @@ -7342,7 +7344,9 @@ 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. +.new The default is &"lax"&. +.wen See also the &$lookup_dnssec_authenticated$& variable. @@ -13443,7 +13447,7 @@ 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 +.new .vitem &$tls_out_cipher_std$& .vindex "&$tls_out_cipher_std$&" As above, but returning the RFC standard name for the cipher suite. @@ -14679,8 +14683,10 @@ 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 @@ -15464,12 +15470,14 @@ not also supplied, the gid is taken from the result of &[getpwnam()]& if it is used. See chapter &<>& for a discussion of security issues. +.new .option exim_version main string "current version" .cindex "Exim version" .cindex customizing "version number" .cindex "version number of Exim" override -This option allows to override the &$version_number$&/&$exim_version$& Exim reports in -various places. Use with care, this may fool stupid security scanners. +This option overrides the &$version_number$&/&$exim_version$& that Exim reports in +various places. Use with care; this may fool stupid security scanners. +.wen .option extra_local_interfaces main "string list" unset @@ -16443,9 +16451,9 @@ 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 @@ -16956,12 +16964,6 @@ 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 add_environment main "string list" empty -.cindex "environment" -This option allows to add 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" @@ -19152,7 +19154,7 @@ 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 $"name = value"$ +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, @@ -19163,7 +19165,7 @@ The variables can be used by the router options (not including any preconditions) and by the transport. Later definitions of a given named variable will override former ones. -Varible use is via the usual &$r_...$& syntax. +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. @@ -26928,7 +26930,21 @@ 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" +.new +.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. +.wen + +.section "Plaintext server options" "SECID171" .cindex "options" "&(plaintext)& authenticator (server)" When configured as a server, &(plaintext)& uses the following options: @@ -26936,7 +26952,7 @@ 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. @@ -27751,6 +27767,7 @@ msn: . //////////////////////////////////////////////////////////////////////////// . //////////////////////////////////////////////////////////////////////////// +.new .chapter "The external authenticator" "CHAPexternauth" .scindex IIDexternauth1 "&(external)& authenticator" .scindex IIDexternauth2 "authenticators" "&(external)&" @@ -27852,11 +27869,10 @@ 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" @@ -27880,6 +27896,7 @@ ext_ccert: .ecindex IIDexternauth1 .ecindex IIDexternauth2 +.wen @@ -28069,14 +28086,22 @@ 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. +.new +To build Exim to use OpenSSL you need to set +.code +USE_OPENSSL=yes +.endd +in Local/Makefile. +.wen + +To build Exim to use GnuTLS, you need to set .code USE_GNUTLS=yes .endd -in Local/Makefile -you must also set TLS_LIBS and TLS_INCLUDE appropriately, so that the +in Local/Makefile. + +You must also set TLS_LIBS and TLS_INCLUDE appropriately, so that the include files and libraries for GnuTLS can be found. There are some differences in usage when using GnuTLS instead of OpenSSL: @@ -28634,9 +28659,9 @@ if it requests it. If the server is Exim, it will request a certificate only if &%tls_verify_hosts%& or &%tls_try_verify_hosts%& matches the client. .new -Do not use a certificate which has the OCSP-must-staple extension, +&*Note*&: Do not use a certificate which has the OCSP-must-staple extension, for client use (they are usable for server use). -As TLS has no means for the client to staple before TLS 1.3 it will result +As the TLS protocol has no means for the client to staple before TLS 1.3 it will result in failed connections. .wen @@ -29060,7 +29085,7 @@ 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 +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. @@ -29093,7 +29118,7 @@ If DANE is not usable, whether requested or not, and CA-anchored verification evaluation is wanted, the above variables should be set appropriately. The router and transport option &%dnssec_request_domains%& must not be -set to "never" and &%dnssec_require_domains%& is ignored. +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". @@ -30412,6 +30437,13 @@ 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" @@ -34334,9 +34366,9 @@ The second argument is used to request that the data be buffered 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. -Nobody noticed until 4.93 was imminent. -A decision on the way forward has not yet been 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. .wen Strings that are written by &'smtp_printf()'& from within &[local_scan()]& @@ -34368,12 +34400,18 @@ 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. @@ -40567,7 +40605,7 @@ the libopendmarc library is used. For building Exim yourself, obtain the library from &url(http://sourceforge.net/projects/opendmarc/) -to obtain a copy, or find it in your favorite rpm package +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 @@ -40623,7 +40661,7 @@ non-authenticated user. It makes sense to only verify DMARC status of messages coming from remote, untrusted sources. You can use standard conditions such as hosts, senders, etc, to decide that DMARC verification should *not* be performed for them and disable -DMARC with a control setting: +DMARC with an ACL control modifier: .code control = dmarc_disable_verify .endd @@ -40634,15 +40672,15 @@ results in unintended information leakage (what lists a user might be subscribed to, etc). You must configure exim to submit forensic reports to the owner of the domain. If the DMARC record contains a forensic address and you specify the control statement below, then -exim will send these forensic emails. It's also advised that you -configure a dmarc_forensic_sender because the default sender address +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 it to send them, it will not +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 @@ -40651,14 +40689,14 @@ 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" +&"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. +occurs until a &"dmarc_status"& condition is encountered in the ACLs. -The dmarc_status condition takes a list of strings on its +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: @@ -40691,28 +40729,30 @@ Several expansion variables are set before the DATA ACL is processed, and you can use them in this ACL. The following expansion variables are available: -&$dmarc_status$& +.vlist +.vitem &$dmarc_status$& .vindex &$dmarc_status$& .cindex DMARC result -is a one word status indicating what the DMARC library +A one word status indicating what the DMARC library thinks of the email. It is a combination of the results of DMARC record lookup and the SPF/DKIM/DMARC processing results (if a DMARC record was found). The actual policy declared in the DMARC record is in a separate expansion variable. -&$dmarc_status_text$& +.vitem &$dmarc_status_text$& .vindex &$dmarc_status_text$& -is a slightly longer, human readable status. +Slightly longer, human readable status. -&$dmarc_used_domain$& +.vitem &$dmarc_used_domain$& .vindex &$dmarc_used_domain$& -is the domain which DMARC used to look up the DMARC policy record. +The domain which DMARC used to look up the DMARC policy record. -&$dmarc_domain_policy$& +.vitem &$dmarc_domain_policy$& .vindex &$dmarc_domain_policy$& -is the policy declared in the DMARC record. Valid values +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 @@ -40727,7 +40767,7 @@ processing or failure delivery issues). In order to log statistics suitable to be imported by the opendmarc tools, you need to: .ilist -Configure the global setting dmarc_history_file +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 @@ -40735,7 +40775,7 @@ import scripts and truncating the dmarc_history_file In order to send forensic reports, you need to: .ilist -Configure the global setting dmarc_forensic_sender +Configure the global option &%dmarc_forensic_sender%& .next Configure, somewhere before the DATA ACL, the control option to enable sending DMARC forensic reports