X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/82b199b94da8ad79db922e34e2fc457eed4ad5ad..da3ad30dcfbb4770835c2b7e165bb719f76cfc16:/doc/doc-docbook/spec.xfpt?ds=sidebyside diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index 34205b4f4..016f3f075 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -1,5 +1,3 @@ -. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.88 2010/06/14 18:51:09 pdp Exp $ -. . ///////////////////////////////////////////////////////////////////////////// . This is the primary source of the Exim Manual. It is an xfpt document that is . converted into DocBook XML for subsequent conversion into printing and online @@ -47,8 +45,8 @@ . the element must also be updated for each new edition. . ///////////////////////////////////////////////////////////////////////////// -.set previousversion "4.72" -.set version "4.74" +.set previousversion "4.75" +.set version "4.77" .set ACL "access control lists (ACLs)" .set I "    " @@ -172,12 +170,12 @@ Specification of the Exim Mail Transfer Agent The Exim MTA -21 Jan 2011 +06 May 2011 EximMaintainers EM - 4.74 - 21 Jan 2011 + 4.77 + 10 Oct 2011 EM 2011University of Cambridge @@ -470,10 +468,10 @@ first to check that you are not duplicating a previous entry. The following Exim mailing lists exist: .table2 140pt +.row &'exim-announce@exim.org'& "Moderated, low volume announcements list" .row &'exim-users@exim.org'& "General discussion list" .row &'exim-dev@exim.org'& "Discussion of bugs, enhancements, etc." -.row &'exim-announce@exim.org'& "Moderated, low volume announcements list" -.row &'exim-future@exim.org'& "Discussion of long-term development" +.row &'exim-cvs@exim.org'& "Automated commit messages from the VCS" .endtable You can subscribe to these lists, change your existing subscriptions, and view @@ -1541,7 +1539,6 @@ is on a file system where the user is over quota. Exim can be configured to impose its own quotas on local mailboxes; where system quotas are set they will also apply. -.new If a host is unreachable for a period of time, a number of messages may be waiting for it by the time it recovers, and sending them in a single SMTP connection is clearly beneficial. Whenever a delivery to a remote host is @@ -1552,7 +1549,6 @@ SMTP delivery has happened, it looks to see if any other messages are waiting for the same host. If any are found, they are sent over the same SMTP connection, subject to a configuration limit as to the maximum number in any one connection. -.wen @@ -1872,6 +1868,14 @@ SUPPORT_TLS=yes TLS_LIBS=-L/usr/local/openssl/lib -lssl -lcrypto TLS_INCLUDE=-I/usr/local/openssl/include/ .endd +.new +.cindex "pkg-config" "OpenSSL" +If you have &'pkg-config'& available, then instead you can just use: +.code +SUPPORT_TLS=yes +USE_OPENSSL_PC=openssl +.endd +.wen .cindex "USE_GNUTLS" If GnuTLS is installed, you should set .code @@ -1887,6 +1891,16 @@ USE_GNUTLS=yes TLS_LIBS=-L/usr/gnu/lib -lgnutls -ltasn1 -lgcrypt TLS_INCLUDE=-I/usr/gnu/include .endd +.new +.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 +.wen + You do not need to set TLS_INCLUDE if the relevant directory is already specified in INCLUDE. Details of how to configure Exim to make use of TLS are given in chapter &<>&. @@ -1894,7 +1908,6 @@ given in chapter &<>&. -.new .section "Use of tcpwrappers" "SECID27" .cindex "tcpwrappers, building Exim to support" @@ -1927,7 +1940,6 @@ can be changed at build time by setting TCP_WRAPPERS_DAEMON_NAME in in &_Local/Makefile_&, or by setting tcp_wrappers_daemon_name in the configure file. Consult the &'tcpwrappers'& documentation for further details. -.wen .section "Including support for IPv6" "SECID28" @@ -1949,7 +1961,6 @@ support has not been tested for some time. -.new .section "Dynamically loaded lookup module support" "SECTdynamicmodules" .cindex "lookup modules" .cindex "dynamic modules" @@ -1978,7 +1989,7 @@ LOOKUP_LSEARCH=yes LOOKUP_SQLITE=2 LOOKUP_MYSQL=2 .endd -.wen + .section "The building process" "SECID29" .cindex "build directory" @@ -2117,6 +2128,28 @@ files or libraries are required. When a lookup type is not included in the binary, attempts to configure Exim to use it cause run time configuration errors. +.new +.cindex "pkg-config" "lookups" +.cindex "pkg-config" "authenticators" +Many systems now use a tool called &'pkg-config'& to encapsulate information +about how to compile against a library; Exim has some initial support for +being able to use pkg-config for lookups and authenticators. For any given +makefile variable which starts &`LOOKUP_`& or &`AUTH_`&, you can add a new +variable with the &`_PC`& suffix in the name and assign as the value the +name of the package to be queried. The results of querying via the +&'pkg-config'& command will be added to the appropriate Makefile variables +with &`+=`& directives, so your version of &'make'& will need to support that +syntax. For instance: +.code +LOOKUP_SQLITE=yes +LOOKUP_SQLITE_PC=sqlite3 +AUTH_GSASL=yes +AUTH_GSASL_PC=libgsasl +AUTH_HEIMDAL_GSSAPI=yes +AUTH_HEIMDAL_GSSAPI_PC=heimdal-gssapi +.endd +.wen + .cindex "Perl" "including support for" Exim can be linked with an embedded Perl interpreter, allowing Perl subroutines to be called during string expansion. To enable this facility, @@ -2643,12 +2676,10 @@ This option causes Exim to output a few sentences stating what it is. The same output is generated if the Exim binary is called with no options and no arguments. -.new .vitem &%--version%& .oindex "&%--version%&" This option is an alias for &%-bV%& and causes version information to be displayed. -.wen .vitem &%-B%&<&'type'&> .oindex "&%-B%&" @@ -3215,7 +3246,6 @@ above concerning senders and qualification do not apply. In this situation, Exim behaves in exactly the same way as it does when receiving a message via the listening daemon. -.new .vitem &%-bmalware%&&~<&'filename'&> .oindex "&%-bmalware%&" .cindex "testing", "malware" @@ -3235,7 +3265,6 @@ This option requires admin privileges. The &%-bmalware%& option will not be extended to be more generally useful, there are better tools for file-scanning. This option exists to help administrators verify their Exim and AV scanner configuration. -.wen .vitem &%-bt%& .oindex "&%-bt%&" @@ -3283,7 +3312,6 @@ whose behaviour depends on the contents of an incoming message, you cannot test those conditions using &%-bt%&. The &%-N%& option provides a possible way of doing such tests. -.new .vitem &%-bV%& .oindex "&%-bV%&" .cindex "version number of Exim" @@ -3292,7 +3320,7 @@ number, and compilation date of the &'exim'& binary to the standard output. It also lists the DBM library that is being used, the optional modules (such as specific lookup types), the drivers that are included in the binary, and the name of the run time configuration file that is in use. -.wen + As part of its operation, &%-bV%& causes Exim to read and syntax check its configuration file. However, this is a static check only. It cannot check values that are to be expanded. For example, although a misspelt ACL verb is @@ -3370,7 +3398,6 @@ name, but it can be a colon-separated list of names. In this case, the first file that exists is used. Failure to open an existing file stops Exim from proceeding any further along the list, and an error is generated. -.new When this option is used by a caller other than root, and the list is different from the compiled-in list, Exim gives up its root privilege immediately, and runs with the real and effective uid and gid set to those of the caller. @@ -3388,7 +3415,7 @@ running as the Exim user, so when it re-executes to regain privilege for the delivery, the use of &%-C%& causes privilege to be lost. However, root can test reception and delivery using two separate commands (one to put a message on the queue, using &%-odq%&, and another to do the delivery, using &%-M%&). -.wen + If ALT_CONFIG_PREFIX is defined &_in Local/Makefile_&, it specifies a prefix string with which any file named in a &%-C%& command line option must start. In addition, the file name must not contain the sequence &`/../`&. @@ -3418,7 +3445,6 @@ unprivileged caller, it causes Exim to give up its root privilege. If DISABLE_D_OPTION is defined in &_Local/Makefile_&, the use of &%-D%& is completely disabled, and its use causes an immediate error exit. -.new If WHITELIST_D_MACROS is defined in &_Local/Makefile_& then it should be a colon-separated list of macros which are considered safe and, if &%-D%& only supplies macros from this list, and the values are acceptable, then Exim will @@ -3426,7 +3452,7 @@ not give up root privilege if the caller is root, the Exim run-time user, or the CONFIGURE_OWNER, if set. This is a transition mechanism and is expected to be removed in the future. Acceptable values for the macros satisfy the regexp: &`^[A-Za-z0-9_/.-]*$`& -.wen + The entire option (including equals sign if present) must all be within one command line item. &%-D%& can be used to set the value of a macro to the empty string, in which case the equals sign is optional. These two commands are @@ -3821,7 +3847,6 @@ by an admin user. This option causes the contents of the message body (-D) spool file to be written to the standard output. This option can be used only by an admin user. -.new .vitem &%-Mvc%&&~<&'message&~id'&> .oindex "&%-Mvc%&" .cindex "message" "listing in RFC 2822 format" @@ -3829,7 +3854,7 @@ written to the standard output. This option can be used only by an admin user. This option causes a copy of the complete message (header lines plus body) to be written to the standard output in RFC 2822 format. This option can be used only by an admin user. -.wen + .vitem &%-Mvh%&&~<&'message&~id'&> .oindex "&%-Mvh%&" .cindex "listing" "message headers" @@ -4544,7 +4569,6 @@ most configurations, this specifies a single file. However, it is permitted to give a colon-separated list of file names, in which case Exim uses the first existing file in the list. -.new .cindex "EXIM_USER" .cindex "EXIM_GROUP" .cindex "CONFIGURE_OWNER" @@ -4567,7 +4591,7 @@ Up to Exim version 4.72, the run time configuration file was also permitted to be writeable by the Exim user and/or group. That has been changed in Exim 4.73 since it offered a simple privilege escalation for any attacker who managed to compromise the Exim user account. -.wen + A default configuration file, which will work correctly in simple situations, is provided in the file &_src/configure.default_&. If CONFIGURE_FILE defines just one file name, the installation process copies the default @@ -4578,7 +4602,6 @@ configuration. -.new .section "Using a different configuration file" "SECID40" .cindex "configuration file" "alternate" A one-off alternate configuration can be specified by the &%-C%& command line @@ -4601,7 +4624,7 @@ the delivery, the use of &%-C%& causes privilege to be lost. However, root can test reception and delivery using two separate commands (one to put a message on the queue, using &%-odq%&, and another to do the delivery, using &%-M%&). -.wen + If ALT_CONFIG_PREFIX is defined &_in Local/Makefile_&, it specifies a prefix string with which any file named in a &%-C%& command line option must start. In addition, the file name must not contain the sequence &"&`/../`&"&. @@ -4615,7 +4638,6 @@ non-privileged user causes Exim to discard its root privilege. If DISABLE_D_OPTION is defined in &_Local/Makefile_&, the use of &%-D%& is completely disabled, and its use causes an immediate error exit. -.new The WHITELIST_D_MACROS option in &_Local/Makefile_& permits the binary builder to declare certain macro names trusted, such that root privilege will not necessarily be discarded. @@ -4625,7 +4647,6 @@ values are acceptable, then Exim will not give up root privilege if the caller is root, the Exim run-time user, or the CONFIGURE_OWNER, if set. This is a transition mechanism and is expected to be removed in the future. Acceptable values for the macros satisfy the regexp: &`^[A-Za-z0-9_/.-]*$`& -.wen Some sites may wish to use the same Exim binary on different machines that share a file system, but to use different configuration files on each machine. @@ -6202,13 +6223,26 @@ using Berkeley DB versions 3 or 4, it opens existing databases for reading with the DB_UNKNOWN option. This enables it to handle any of the types of database that the library supports, and can be useful for accessing DBM files created by other applications. (For earlier DB versions, DB_HASH is always used.) +.new +.next +.cindex "lookup" "dbmjz" +.cindex "lookup" "dbm &-- embedded NULs" +.cindex "sasldb2" +.cindex "dbmjz lookup type" +&(dbmjz)&: This is the same as &(dbm)&, except that the lookup key is +interpreted as an Exim list; the elements of the list are joined together with +ASCII NUL characters to form the lookup key. An example usage would be to +authenticate incoming SMTP calls using the passwords from Cyrus SASL's +&_/etc/sasldb2_& file with the &(gsasl)& authenticator or Exim's own +&(cram_md5)& authenticator. +.wen .next .cindex "lookup" "dbmnz" .cindex "lookup" "dbm &-- terminating zero" .cindex "binary zero" "in lookup key" .cindex "Courier" .cindex "&_/etc/userdbshadow.dat_&" -.cindex "dmbnz lookup type" +.cindex "dbmnz lookup type" &(dbmnz)&: This is the same as &(dbm)&, except that a terminating binary zero is not included in the key that is passed to the DBM library. You may need this if you want to look up data in files that are created by or shared with some @@ -6885,11 +6919,9 @@ The URL may begin with &`ldap`& or &`ldaps`& if your LDAP library supports secure (encrypted) LDAP connections. The second of these ensures that an encrypted TLS connection is used. -.new With sufficiently modern LDAP libraries, Exim supports forcing TLS over regular LDAP connections, rather than the SSL-on-connect &`ldaps`&. See the &%ldap_start_tls%& option. -.wen .section "LDAP quoting" "SECID68" @@ -7800,7 +7832,7 @@ pattern must be an appropriate query for the lookup type, as described in chapter &<>&. For example: .code hold_domains = mysql;select domain from holdlist \ - where domain = '$domain'; + where domain = '${quote_mysql:$domain}'; .endd In most cases, the data that is looked up is not used (so for an SQL query, for example, it doesn't matter what field you select). Exim is interested only in @@ -8504,6 +8536,13 @@ start of a portion of the string that is interpreted and replaced as described below in section &<>& onwards. Backslash is used as an escape character, as described in the following section. +Whether a string is expanded depends upon the context. Usually this is solely +dependent upon the option for which a value is sought; in this documentation, +options for which string expansion is performed are marked with † after +the data type. ACL rules always expand strings. A couple of expansion +conditions do not expand some of the brace-delimited branches, for security +reasons. + .section "Literal text in expanded strings" "SECTlittext" @@ -9709,7 +9748,6 @@ srandomdev() or srandom(), or a custom implementation even weaker than random(). -.new .vitem &*${reverse_ip:*&<&'ipaddr'&>&*}*& .cindex "expansion" "IP address" This operator reverses an IP address; for IPv4 addresses, the result is in @@ -9723,7 +9761,6 @@ returns .code 4.2.0.192 and 3.0.2.0.0.0.0.c.d.c.b.a.1.0.0.0.9.0.0.0.2.4.c.0.8.b.d.0.1.0.0.2 .endd -.wen .vitem &*${rfc2047:*&<&'string'&>&*}*& @@ -9887,15 +9924,21 @@ lower case), signifying multiplication by 1024 or 1024*1024, respectively. As a special case, the numerical value of an empty string is taken as zero. +In all cases, a relative comparator OP is testing if <&'string1'&> OP +<&'string2'&>; the above example is checking if &$message_size$& is larger than +10M, not if 10M is larger than &$message_size$&. + -.new .vitem &*bool&~{*&<&'string'&>&*}*& .cindex "expansion" "boolean parsing" .cindex "&%bool%& expansion condition" This condition turns a string holding a true or false representation into a boolean state. It parses &"true"&, &"false"&, &"yes"& and &"no"& (case-insensitively); also positive integer numbers map to true if non-zero, -false if zero. Leading and trailing whitespace is ignored. +false if zero. +An empty string is treated as false. +Leading and trailing whitespace is ignored; +thus a string consisting only of whitespace is false. All other string values will result in expansion failure. When combined with ACL variables, this expansion condition will let you @@ -9904,10 +9947,8 @@ For example: .code ${if bool{$acl_m_privileged_sender} ... .endd -.wen -.new .vitem &*bool_lax&~{*&<&'string'&>&*}*& .cindex "expansion" "boolean parsing" .cindex "&%bool_lax%& expansion condition" @@ -9918,7 +9959,7 @@ and the values &"false"&, &"no"& and &"0"& map to false, all others map to true. Leading and trailing whitespace is ignored. Note that where &"bool{00}"& is false, &"bool_lax{00}"& is true. -.wen + .vitem &*crypteq&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& .cindex "expansion" "encrypted comparison" .cindex "encrypted strings, comparing" @@ -10105,6 +10146,25 @@ string is lexically greater than the second string. For &%gt%& the comparison includes the case of letters, whereas for &%gti%& the comparison is case-independent. +.new +.vitem &*inlist&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& &&& + &*inlisti&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& +.cindex "string" "comparison" +.cindex "list" "iterative conditions" +Both strings are expanded; the second string is treated as a list of simple +strings; if the first string is a member of the second, then the condition +is true. + +These are simpler to use versions of the more powerful &*forany*& condition. +Examples, and the &*forany*& equivalents: +.code +${if inlist{needle}{foo:needle:bar}} + ${if forany{foo:needle:bar}{eq{$item}{needle}}} +${if inlisti{Needle}{fOo:NeeDLE:bAr}} + ${if forany{fOo:NeeDLE:bAr}{eqi{$item}{Needle}}} +.endd +.wen + .vitem &*isip&~{*&<&'string'&>&*}*& &&& &*isip4&~{*&<&'string'&>&*}*& &&& &*isip6&~{*&<&'string'&>&*}*& @@ -10215,10 +10275,12 @@ See &*match_local_part*&. .vitem &*match_ip&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& .cindex "&%match_ip%& expansion condition" +.new This condition matches an IP address to a list of IP address patterns. It must be followed by two argument strings. The first (after expansion) must be an IP -address or an empty string. The second (after expansion) is a restricted host +address or an empty string. The second (not expanded) is a restricted host list that can match only an IP address, not a host name. For example: +.wen .code ${if match_ip{$sender_host_address}{1.2.3.4:5.6.7.8}{...}{...}} .endd @@ -10264,6 +10326,11 @@ just as easy to use the fact that a lookup is itself a condition, and write: .endd .endlist ilist +.new +Note that <&'string2'&> is not itself subject to string expansion, unless +Exim was built with the EXPAND_LISTMATCH_RHS option. +.wen + Consult section &<>& for further details of these patterns. .vitem &*match_local_part&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& @@ -10291,6 +10358,11 @@ item can be used, as in all address lists, to cause subsequent items to have their local parts matched casefully. Domains are always matched caselessly. +.new +Note that <&'string2'&> is not itself subject to string expansion, unless +Exim was built with the EXPAND_LISTMATCH_RHS option. +.wen + &*Note*&: Host lists are &'not'& supported in this way. This is because hosts have two identities: a name and an IP address, and it is not clear how to specify cleanly how such a test would work. However, IP addresses can be @@ -10636,6 +10708,15 @@ is empty and &$authentication_failed$& is set to &"1"&). Failure includes any negative response to an AUTH command, including (for example) an attempt to use an undefined mechanism. +.new +.vitem &$av_failed$& +.cindex "content scanning" "AV scanner failure" +This variable is available when Exim is compiled with the content-scanning +extension. It is set to &"0"& by default, but will be set to &"1"& if any +problem occurs with the virus scanner (specified by &%av_scanner%&) during +the ACL malware condition. +.wen + .vitem &$body_linecount$& .cindex "message body" "line count" .cindex "body of message" "line count" @@ -10649,7 +10730,7 @@ number of lines in the message's body. See also &$message_linecount$&. .cindex "binary zero" "in message body" .vindex "&$body_zerocount$&" When a message is being received or delivered, this variable contains the -number of binary zero bytes in the message's body. +number of binary zero bytes (ASCII NULs) in the message's body. .vitem &$bounce_recipient$& .vindex "&$bounce_recipient$&" @@ -11139,13 +11220,11 @@ routers, and transports run) the count is increased to include the lines that are added by ACLs. The blank line that separates the message header from the body is not counted. -.new As with the special case of &$message_size$&, during the expansion of the appendfile transport's maildir_tag option in maildir format, the value of &$message_linecount$& is the precise size of the number of newlines in the file that has been written (minus one for the blank line between the header and the body). -.wen Here is an example of the use of this variable in a DATA ACL: .code @@ -11769,6 +11848,16 @@ command in a filter file. Its use is explained in the description of that command, which can be found in the separate document entitled &'Exim's interfaces to mail filtering'&. +.new +.vitem &$tls_bits$& +.vindex "&$tls_bits$&" +Contains an approximation of the TLS cipher's bit-strength; the meaning of +this depends upon the TLS implementation used. +If TLS has not been negotiated, the value will be 0. +The value of this is automatically fed into the Cyrus SASL authenticator +when acting as a server, to specify the "external SSF" (a SASL term). +.wen + .vitem &$tls_certificate_verified$& .vindex "&$tls_certificate_verified$&" This variable is set to &"1"& if a TLS certificate was verified when the @@ -12695,6 +12784,7 @@ See also the &'Policy controls'& section above. .row &%dns_ipv4_lookup%& "only v4 lookup for these domains" .row &%dns_retrans%& "parameter for resolver" .row &%dns_retry%& "parameter for resolver" +.row &%dns_use_edns0%& "parameter for resolver" .row &%hold_domains%& "hold delivery for these domains" .row &%local_interfaces%& "for routing checks" .row &%queue_domains%& "no immediate delivery for these" @@ -12947,7 +13037,7 @@ saying &"keep on trying, even though there are big problems"&. &%ignore_bounce_errors_after%&. It is retained for compatibility, but it is not thought to be very useful any more, and its use should probably be avoided. -.new + .option av_scanner main string "see below" This option is available if Exim is built with the content-scanning extension. It specifies which anti-virus scanner to use. The default value is: @@ -12956,7 +13046,6 @@ sophie:/var/run/sophie .endd If the value of &%av_scanner%& starts with a dollar character, it is expanded before use. See section &<>& for further details. -.wen .option bi_command main string unset @@ -13061,7 +13150,7 @@ section &<>& for details of the caching. This option defines the &"random"& local part that can be used as part of callout verification. The default value is .code -$primary_host_name-$tod_epoch-testing +$primary_hostname-$tod_epoch-testing .endd See section &<>& for details of how this value is used. @@ -13328,6 +13417,19 @@ to set in them. See &%dns_retrans%& above. +.new +.option dns_use_edns0 main integer -1 +.cindex "DNS" "resolver options" +.cindex "DNS" "EDNS0" +If this option is set to a non-negative number then Exim will initialise the +DNS resolver library to either use or not use EDNS0 extensions, overriding +the system default. A value of 0 coerces EDNS0 off, a value of 1 coerces EDNS0 +on. + +If the resolver library does not support EDNS0 then this option has no effect. +.wen + + .option drop_cr main boolean false This is an obsolete option that is now a no-op. It used to affect the way Exim handled CR and LF characters in incoming messages. What happens now is @@ -13827,7 +13929,6 @@ next attempt to deliver such a message, it gets removed. The incident is logged. -.new .option ldap_ca_cert_dir main string unset .cindex "LDAP", "TLS CA certificate directory" This option indicates which directory contains CA certificates for verifying @@ -13835,10 +13936,8 @@ a TLS certificate presented by an LDAP server. While Exim does not provide a default value, your SSL library may. Analogous to &%tls_verify_certificates%& but as a client-side option for LDAP and constrained to be a directory. -.wen -.new .option ldap_ca_cert_file main string unset .cindex "LDAP", "TLS CA certificate file" This option indicates which file contains CA certificates for verifying @@ -13846,35 +13945,28 @@ a TLS certificate presented by an LDAP server. While Exim does not provide a default value, your SSL library may. Analogous to &%tls_verify_certificates%& but as a client-side option for LDAP and constrained to be a file. -.wen -.new .option ldap_cert_file main string unset .cindex "LDAP" "TLS client certificate file" This option indicates which file contains an TLS client certificate which Exim should present to the LDAP server during TLS negotiation. Should be used together with &%ldap_cert_key%&. -.wen -.new .option ldap_cert_key main string unset .cindex "LDAP" "TLS client key file" This option indicates which file contains the secret/private key to use to prove identity to the LDAP server during TLS negotiation. Should be used together with &%ldap_cert_file%&, which contains the identity to be proven. -.wen -.new .option ldap_cipher_suite main string unset .cindex "LDAP" "TLS cipher suite" This controls the TLS cipher-suite negotiation during TLS negotiation with the LDAP server. See &<>& for more details of the format of cipher-suite options with OpenSSL (as used by LDAP client libraries). -.wen .option ldap_default_servers main "string list" unset @@ -13885,7 +13977,6 @@ details of LDAP queries. This option is available only when Exim has been built with LDAP support. -.new .option ldap_require_cert main string unset. .cindex "LDAP" "policy for LDAP server TLS cert presentation" This should be one of the values "hard", "demand", "allow", "try" or "never". @@ -13893,10 +13984,8 @@ A value other than one of these is interpreted as "never". See the entry "TLS_REQCERT" in your system man page for ldap.conf(5). Although Exim does not set a default, the LDAP library probably defaults to hard/demand. -.wen -.new .option ldap_start_tls main boolean false .cindex "LDAP" "whether or not to negotiate TLS" If set, Exim will attempt to negotiate TLS with the LDAP server when @@ -13905,7 +13994,6 @@ connecting on a regular LDAP port. This is the LDAP equivalent of SMTP's of SSL-on-connect. In the event of failure to negotiate TLS, the action taken is controlled by &%ldap_require_cert%&. -.wen .option ldap_version main integer unset @@ -14181,7 +14269,6 @@ an oversized message is logged in both the main and the reject logs. See also the generic transport option &%message_size_limit%&, which limits the size of message that an individual transport can process. -.new If you use a virus-scanner and set this option to to a value larger than the maximum size that your virus-scanner is configured to support, you may get failures triggered by large mails. The right size to configure for the @@ -14189,7 +14276,10 @@ virus-scanner depends upon what data is passed and the options in use but it's probably safest to just set it to a little larger than this value. Eg, with a default Exim message size of 50M and a default ClamAV StreamMaxLength of 10M, some problems may result. -.wen + +A value of 0 will disable size limit checking; Exim will still advertise the +SIZE extension in an EHLO response, but without a limit, so as to permit +SMTP clients to still indicate the message size along with the MAIL verb. .option move_frozen_messages main boolean false @@ -14243,17 +14333,12 @@ harm. This option overrides the &%pipe_as_creator%& option of the &(pipe)& transport driver. -.new -.option openssl_options main "string list" +dont_insert_empty_fragments +.option openssl_options main "string list" unset .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, -each one to be +added or -subtracted from the current value. The default -value is one option which happens to have been set historically. You can -remove all options with: -.code -openssl_options = -all -.endd +each one to be +added or -subtracted from the current value. + This option is only available if Exim is built against OpenSSL. The values available for this option vary according to the age of your OpenSSL install. The &"all"& value controls a subset of flags which are available, typically @@ -14265,14 +14350,75 @@ names lose the leading &"SSL_OP_"& and are lower-cased. Note that adjusting the options can have severe impact upon the security of SSL as used by Exim. It is possible to disable safety checks and shoot yourself in the foot in various unpleasant ways. This option should not be -adjusted lightly. An unrecognised item will be detected at by invoking Exim -with the &%-bV%& flag. +adjusted lightly. An unrecognised item will be detected at startup, by +invoking Exim with the &%-bV%& flag. + +.new +Historical note: prior to release 4.78, Exim defaulted this value to +"+dont_insert_empty_fragments", which may still be needed for compatibility +with some clients, but which lowers security by increasing exposure to +some now infamous attacks. +.wen An example: .code -openssl_options = -all +microsoft_big_sslv3_buffer +openssl_options = -all +microsoft_big_sslv3_buffer +dont_insert_empty_fragments .endd -.wen + +Possible options may include: +.ilist +&`all`& +.ilist +&`allow_unsafe_legacy_renegotiation`& +.ilist +&`cipher_server_preference`& +.ilist +&`dont_insert_empty_fragments`& +.ilist +&`ephemeral_rsa`& +.ilist +&`legacy_server_connect`& +.ilist +&`microsoft_big_sslv3_buffer`& +.ilist +&`microsoft_sess_id_bug`& +.ilist +&`msie_sslv2_rsa_padding`& +.ilist +&`netscape_challenge_bug`& +.ilist +&`netscape_reuse_cipher_change_bug`& +.ilist +&`no_compression`& +.ilist +&`no_session_resumption_on_renegotiation`& +.ilist +&`no_sslv2`& +.ilist +&`no_sslv3`& +.ilist +&`no_ticket`& +.ilist +&`no_tlsv1`& +.ilist +&`no_tlsv1_1`& +.ilist +&`no_tlsv1_2`& +.ilist +&`single_dh_use`& +.ilist +&`single_ecdh_use`& +.ilist +&`ssleay_080_client_dh_bug`& +.ilist +&`sslref2_reuse_cert_type_bug`& +.ilist +&`tls_block_padding_bug`& +.ilist +&`tls_d5_bug`& +.ilist +&`tls_rollback_bug`& +.endlist .option oracle_servers main "string list" unset @@ -15375,7 +15521,7 @@ contains the pipe command. This specifies the transport driver that is to be used when a &%mail%& command is used in a system filter. -.new + .option system_filter_user main string unset .cindex "uid (user id)" "system filter" If this option is set to root, the system filter is run in the main Exim @@ -15390,7 +15536,6 @@ specified by &%system_filter_group%&. When the uid is specified numerically, If the system filter generates any pipe, file, or reply deliveries, the uid under which the filter is run is used when transporting them, unless a transport option overrides. -.wen .option tcp_nodelay main boolean true @@ -15535,14 +15680,13 @@ are using OpenSSL, you can set &%tls_verify_certificates%& to the name of a directory containing certificate files. This does not work with GnuTLS; the option must be set to the name of a single file if you are using GnuTLS. -.new These certificates should be for the certificate authorities trusted, rather than the public cert of individual clients. With both OpenSSL and GnuTLS, if the value is a file then the certificates are sent by Exim as a server to connecting clients, defining the list of accepted certificate authorities. Thus the values defined should be considered public data. To avoid this, use OpenSSL with a directory. -.wen + .option tls_verify_hosts main "host list&!!" unset .cindex "TLS" "client certificate verification" @@ -15880,12 +16024,9 @@ router is skipped, and the address is offered to the next one. If the result is any other value, the router is run (as this is the last precondition to be evaluated, all the other preconditions must be true). -.new This option is unique in that multiple &%condition%& options may be present. All &%condition%& options must succeed. -.wen -.new The &%condition%& option provides a means of applying custom conditions to the running of routers. Note that in the case of a simple conditional expansion, the default expansion values are exactly what is wanted. For example: @@ -15907,7 +16048,6 @@ condition = foobar If the expansion fails (other than forced failure) delivery is deferred. Some of the other precondition options are common special cases that could in fact be specified using &%condition%&. -.wen .option debug_print routers string&!! unset @@ -19985,13 +20125,16 @@ This option applies only to deliveries in maildir format, and is described in section &<>& below. -.option maildir_use_size_file appendfile boolean false +.new +.option maildir_use_size_file appendfile&!! boolean false .cindex "maildir format" "&_maildirsize_& file" -Setting this option true enables support for &_maildirsize_& files. Exim +The result of string expansion for this option must be a valid boolean value. +If it is true, it enables support for &_maildirsize_& files. Exim creates a &_maildirsize_& file in a maildir if one does not exist, taking the quota from the &%quota%& option of the transport. If &%quota%& is unset, the value is zero. See &%maildir_quota_directory_regex%& above and section &<>& below for further details. +.wen .option maildirfolder_create_regex appendfile string unset .cindex "maildir format" "&_maildirfolder_& file" @@ -20607,7 +20750,7 @@ tag is added to its name. However, if adding the tag takes the length of the name to the point where the test &[stat()]& call fails with ENAMETOOLONG, the tag is dropped and the maildir file is created with no tag. -.new + .vindex "&$message_size$&" Tags can be used to encode the size of files in their names; see &%quota_size_regex%& above for an example. The expansion of &%maildir_tag%& @@ -20630,7 +20773,6 @@ but you should check the documentation of the other software to be sure. It is advisable to also set &%quota_size_regex%& when setting &%maildir_tag%& as this allows Exim to extract the size from your tag, instead of having to &[stat()]& each message file. -.wen .section "Using a maildirsize file" "SECID136" @@ -21272,14 +21414,12 @@ is set, failure to exec is treated specially, and causes the message to be frozen, whatever the setting of &%ignore_status%&. -.new -.otion freeze_signal pipe boolean false +.option freeze_signal pipe boolean false .cindex "signal exit" -.cidenx "&(pipe)& transport", "signal exit" +.cindex "&(pipe)& transport", "signal exit" Normally if the process run by a command in a pipe transport exits on a signal, a bounce message is sent. If &%freeze_signal%& is set, the message will be frozen in Exim's queue instead. -.wen .option ignore_status pipe boolean false @@ -21369,7 +21509,6 @@ sought in the PATH directories, in the usual way. &*Warning*&: This does not apply to a command specified as a transport filter. -.new .option permit_coredump pipe boolean false Normally Exim inhibits core-dumps during delivery. If you have a need to get a core-dump of a pipe command, enable this command. This enables core-dumps @@ -21379,7 +21518,6 @@ for it and that this only be enabled when needed, as the risk of excessive resource consumption can be quite high. Note also that Exim is typically installed as a setuid binary and most operating systems will inhibit coredumps of these by default, so further OS-specific action may be required. -.wen .option pipe_as_creator pipe boolean false @@ -22088,12 +22226,22 @@ is deferred. .option protocol smtp string smtp .cindex "LMTP" "over TCP/IP" +.cindex "ssmtp protocol" "outbound" +.cindex "TLS" "SSL-on-connect outbound" +.vindex "&$port$&" If this option is set to &"lmtp"& instead of &"smtp"&, the default value for the &%port%& option changes to &"lmtp"&, and the transport operates the LMTP protocol (RFC 2033) instead of SMTP. This protocol is sometimes used for local deliveries into closed message stores. Exim also has support for running LMTP over a pipe to a local process &-- see chapter &<>&. +.new +If this option is set to &"smtps"&, the default vaule for the &%port%& option +changes to &"smtps"&, and the transport initiates TLS immediately after +connecting, as an outbound SSL-on-connect, instead of using STARTTLS to upgrade. +The Internet standards bodies strongly discourage use of this mode. +.wen + .option retry_include_ip_address smtp boolean true Exim normally includes both the host name and the IP address in the key it @@ -23380,15 +23528,29 @@ included by setting .code AUTH_CRAM_MD5=yes AUTH_CYRUS_SASL=yes +.new +AUTH_DOVECOT=yes +AUTH_GSASL=yes +AUTH_HEIMDAL_GSSAPI=yes +.wen AUTH_PLAINTEXT=yes AUTH_SPA=yes .endd in &_Local/Makefile_&, respectively. The first of these supports the CRAM-MD5 authentication mechanism (RFC 2195), and the second provides an interface to -the Cyrus SASL authentication library. The third can be configured to support +the Cyrus SASL authentication library. +.new +The third is an interface to Dovecot's authentication system, delegating the +work via a socket interface. +The fourth provides an interface to the GNU SASL authentication library, which +provides mechanisms but typically not data sources. +The fifth provides direct access to Heimdal GSSAPI, geared for Kerberos, but +supporting setting a server keytab. +The sixth can be configured to support the PLAIN authentication mechanism (RFC 2595) or the LOGIN mechanism, which is -not formally documented, but used by several MUAs. The fourth authenticator +not formally documented, but used by several MUAs. The seventh authenticator supports Microsoft's &'Secure Password Authentication'& mechanism. +.wen The authenticators are configured using the same syntax as other drivers (see section &<>&). If no authenticators are required, no @@ -23420,6 +23582,30 @@ The remainder of this chapter covers the generic options for the authenticators, followed by general discussion of the way authentication works in Exim. +.new +&*Beware:*& the meaning of &$auth1$&, &$auth2$&, ... varies on a per-driver and +per-mechanism basis. Please read carefully to determine which variables hold +account labels such as usercodes and which hold passwords or other +authenticating data. + +Note that some mechanisms support two different identifiers for accounts: the +&'authentication id'& and the &'authorization id'&. The contractions &'authn'& +and &'authz'& are commonly encountered. The American spelling is standard here. +Conceptually, authentication data such as passwords are tied to the identifier +used to authenticate; servers may have rules to permit one user to act as a +second user, so that after login the session is treated as though that second +user had logged in. That second user is the &'authorization id'&. A robust +configuration might confirm that the &'authz'& field is empty or matches the +&'authn'& field. Often this is just ignored. The &'authn'& can be considered +as verified data, the &'authz'& as an unverified request which the server might +choose to honour. + +A &'realm'& is a text string, typically a domain name, presented by a server +to a client to help it select an account and credentials to use. In some +mechanisms, the client and server provably agree on the realm, but clients +typically can not treat the realm as secure data to be blindly trusted. +.wen + .section "Generic options for authenticators" "SECID168" @@ -23466,6 +23652,11 @@ This option must be set for a &%plaintext%& server authenticator, where it is used directly to control authentication. See section &<>& for details. +.new +For the &(gsasl)& authenticator, this option is required for various +mechanisms; see chapter &<>& for details. +.wen + For the other authenticators, &%server_condition%& can be used as an additional authentication or authorization mechanism that is applied after the other authenticator conditions succeed. If it is set, it is expanded when the @@ -23914,7 +24105,6 @@ with the AUTH command (in contravention of the specification of LOGIN), but if the client does not supply it (as is the case for LOGIN clients), the prompt strings are used to obtain two data items. -.new Some clients are very particular about the precise text of the prompts. For example, Outlook Express is reported to recognize only &"Username:"& and &"Password:"&. Here is an example of a LOGIN authenticator that uses those @@ -23939,7 +24129,7 @@ operator to correctly quote the DN for authentication. However, the basic correct one to use for the password, because quoting is needed only to make the password conform to the Exim syntax. At the LDAP level, the password is an uninterpreted string. -.wen + .section "Support for different kinds of authentication" "SECID174" A number of string expansion features are provided for the purpose of @@ -24071,6 +24261,20 @@ lookup_cram: Note that this expansion explicitly forces failure if the lookup fails because &$auth1$& contains an unknown user name. +.new +As another example, if you wish to re-use a Cyrus SASL sasldb2 file without +using the relevant libraries, you need to know the realm to specify in the +lookup and then ask for the &"userPassword"& attribute for that user in that +realm, with: +.code +cyrusless_crammd5: + driver = cram_md5 + public_name = CRAM-MD5 + server_secret = ${lookup{$auth1:mail.example.org:userPassword}\ + dbmjz{/etc/sasldb2}} + server_set_id = $auth1 +.endd +.wen .section "Using cram_md5 as a client" "SECID177" .cindex "options" "&(cram_md5)& authenticator (client)" @@ -24144,10 +24348,17 @@ be set in &_exim.conf_& in your SASL directory. If you are using GSSAPI for Kerberos, note that because of limitations in the GSSAPI interface, changing the server keytab might need to be communicated down to the Kerberos layer independently. The mechanism for doing so is dependent upon the Kerberos -implementation. For example, for Heimdal, the environment variable KRB5_KTNAME +implementation. +.new +For example, for older releases of Heimdal, the environment variable KRB5_KTNAME may be set to point to an alternative keytab file. Exim will pass this variable through from its own inherited environment when started as root or the Exim user. The keytab file needs to be readable by the Exim user. +With newer releases of Heimdal, a setuid Exim may cause Heimdal to discard the +environment variable. In practice, for those releases, the Cyrus authenticator +is not a suitable interface for GSSAPI (Kerberos) support. Instead, consider +the &(heimdal_gssapi)& authenticator, described in chapter &<>& +.wen .section "Using cyrus_sasl as a server" "SECID178" @@ -24178,8 +24389,10 @@ sasl: server_set_id = $auth1 .endd -.option server_realm cyrus_sasl string unset +.new +.option server_realm cyrus_sasl string&!! unset This specifies the SASL realm that the server claims to be in. +.wen .option server_service cyrus_sasl string &`smtp`& @@ -24250,6 +24463,217 @@ who authenticated is placed in &$auth1$&. .ecindex IIDdcotauth2 +. //////////////////////////////////////////////////////////////////////////// +. //////////////////////////////////////////////////////////////////////////// +.new +.chapter "The gsasl authenticator" "CHAPgsasl" +.scindex IIDgsaslauth1 "&(gsasl)& authenticator" +.scindex IIDgsaslauth2 "authenticators" "&(gsasl)&" +.cindex "authentication" "GNU SASL" +.cindex "authentication" "SASL" +.cindex "authentication" "EXTERNAL" +.cindex "authentication" "ANONYMOUS" +.cindex "authentication" "PLAIN" +.cindex "authentication" "LOGIN" +.cindex "authentication" "DIGEST-MD5" +.cindex "authentication" "CRAM-MD5" +.cindex "authentication" "SCRAM-SHA-1" +The &(gsasl)& authenticator provides server integration for the GNU SASL +library and the mechanisms it provides. This is new as of the 4.78 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. + + +.option server_channelbinding gsasl bool false +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 +authentication process if that context differs. Specifically, some TLS +ciphersuites can provide identifying information about the cryptographic +context. + +This means 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 +only usable by mechanisms which support "channel binding"; at time of +writing, that's the SCRAM family. + +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 may switch the default to be true. + + +.option server_hostname gsasl string&!! "see below" +This option selects the hostname that is used when communicating with the +library. The default value is &`$primary_hostname`&. +Some mechanisms will use this data. + + +.option server_mech gsasl string "see below" +This option selects the authentication mechanism this driver should use. The +default is the value of the generic &%public_name%& option. This option allows +you to use a different underlying mechanism from the advertised name. For +example: +.code +sasl: + driver = gsasl + public_name = X-ANYTHING + server_mech = CRAM-MD5 + server_set_id = $auth1 +.endd + + +.option server_password gsasl string&!! unset +Various mechanisms need access to the cleartext password on the server, so +that proof-of-possession can be demonstrated on the wire, without sending +the password itself. + +The data available for lookup varies per mechanism. +In all cases, &$auth1$& is set to the &'authentication id'&. +The &$auth2$& variable will always be the &'authorization id'& (&'authz'&) +if available, else the empty string. +The &$auth3$& variable will always be the &'realm'& if available, +else the empty string. + +A forced failure will cause authentication to defer. + +If using this option, it may make sense to set the &%server_condition%& +option to be simply "true". + + +.option server_realm gsasl string&!! unset +This specifies the SASL realm that the server claims to be in. +Some mechanisms will use this data. + + +.option server_scram_iter gsasl string&!! unset +This option provides data for the SCRAM family of mechanisms. +&$auth1$& is not available at evaluation time. +(This may change, as we receive feedback on use) + + +.option server_scram_salt gsasl string&!! unset +This option provides data for the SCRAM family of mechanisms. +&$auth1$& is not available at evaluation time. +(This may change, as we receive feedback on use) + + +.option server_service gsasl string &`smtp`& +This is the SASL service that the server claims to implement. +Some mechanisms will use this data. + + +.section "&(gsasl)& auth variables" "SECTgsaslauthvar" +.vindex "&$auth1$&, &$auth2$&, etc" +These may be set when evaluating specific options, as detailed above. +They will also be set when evaluating &%server_condition%&. + +Unless otherwise stated below, the &(gsasl)& integration will use the following +meanings for these variables: + +.ilist +.vindex "&$auth1$&" +&$auth1$&: the &'authentication id'& +.next +.vindex "&$auth2$&" +&$auth2$&: the &'authorization id'& +.next +.vindex "&$auth3$&" +&$auth3$&: the &'realm'& +.endlist + +On a per-mechanism basis: + +.ilist +.cindex "authentication" "EXTERNAL" +EXTERNAL: only &$auth1$& is set, to the possibly empty &'authorization id'&; +the &%server_condition%& option must be present. +.next +.cindex "authentication" "ANONYMOUS" +ANONYMOUS: only &$auth1$& is set, to the possibly empty &'anonymous token'&; +the &%server_condition%& option must be present. +.next +.cindex "authentication" "GSSAPI" +GSSAPI: &$auth1$& will be set to the &'GSSAPI Display Name'&; +&$auth2$& will be set to the &'authorization id'&, +the &%server_condition%& option must be present. +.endlist + +An &'anonymous token'& is something passed along as an unauthenticated +identifier; this is analogous to FTP anonymous authentication passing an +email address, or software-identifier@, as the "password". + + +An example showing the password having the realm specified in the callback +and demonstrating a Cyrus SASL to GSASL migration approach is: +.code +gsasl_cyrusless_crammd5: + driver = gsasl + public_name = CRAM-MD5 + server_realm = imap.example.org + server_password = ${lookup{$auth1:$auth3:userPassword}\ + dbmjz{/etc/sasldb2}{$value}fail} + server_set_id = ${quote:$auth1} + server_condition = yes +.endd + +.wen + +. //////////////////////////////////////////////////////////////////////////// +. //////////////////////////////////////////////////////////////////////////// + +.new +.chapter "The heimdal_gssapi authenticator" "CHAPheimdalgss" +.scindex IIDheimdalgssauth1 "&(heimdal_gssapi)& authenticator" +.scindex IIDheimdalgssauth2 "authenticators" "&(heimdal_gssapi)&" +.cindex "authentication" "GSSAPI" +.cindex "authentication" "Kerberos" +The &(heimdal_gssapi)& authenticator provides server integration for the +Heimdal GSSAPI/Kerberos library, permitting Exim to set a keytab pathname +reliably. + +.option server_hostname heimdal_gssapi string&!! "see below" +This option selects the hostname that is used, with &%server_service%&, +for constructing the GSS server name, as a &'GSS_C_NT_HOSTBASED_SERVICE'& +identifier. The default value is &`$primary_hostname`&. + +.option server_keytab heimdal_gssapi string&!! unset +If set, then Heimdal will not use the system default keytab (typically +&_/etc/krb5.keytab_&) but instead the pathname given in this option. +The value should be a pathname, with no &"file:"& prefix. + +.option server_service heimdal_gssapi string&!! "smtp" +This option specifies the service identifier used, in conjunction with +&%server_hostname%&, for building the identifer for finding credentials +from the keytab. + + +.section "&(heimdal_gssapi)& auth variables" "SECTheimdalgssauthvar" +Beware that these variables will typically include a realm, thus will appear +to be roughly like an email address already. The &'authzid'& in &$auth2$& is +not verified, so a malicious client can set it to anything. + +The &$auth1$& field should be safely trustable as a value from the Key +Distribution Center. Note that these are not quite email addresses. +Each identifier is for a role, and so the left-hand-side may include a +role suffix. For instance, &"joe/admin@EXAMPLE.ORG"&. + +.vindex "&$auth1$&, &$auth2$&, etc" +.ilist +.vindex "&$auth1$&" +&$auth1$&: the &'authentication id'&, set to the GSS Display Name. +.next +.vindex "&$auth2$&" +&$auth2$&: the &'authorization id'&, sent within SASL encapsulation after +authentication. If that was empty, this will also be set to the +GSS Display Name. +.endlist + +.wen + . //////////////////////////////////////////////////////////////////////////// . //////////////////////////////////////////////////////////////////////////// @@ -24614,8 +25038,14 @@ DHE_DSS). The default list contains RSA, DHE_DSS, DHE_RSA. For &%gnutls_require_mac%&, the recognized names are SHA (synonym SHA1), and MD5. The default list contains SHA, MD5. -For &%gnutls_require_protocols%&, the recognized names are TLS1 and SSL3. -The default list contains TLS1, SSL3. +.new +For &%gnutls_require_protocols%&, the recognized names are TLS1.2, TLS1.1, +TLS1.0, (TLS1) and SSL3. +The default list contains TLS1.2, TLS1.1, TLS1.0, SSL3. +TLS1 is an alias for TLS1.0, for backwards compatibility. +For sufficiently old versions of the GnuTLS library, TLS1.2 or TLS1.1 might +not be supported and will not be recognised by Exim. +.wen In a server, the order of items in these lists is unimportant. The server advertises the availability of all the relevant cipher suites. However, in a @@ -25139,7 +25569,6 @@ and try again later, but that is their problem, though it does waste some of your resources. -.new .section "The SMTP DKIM ACL" "SECTDKIMACL" The &%acl_smtp_dkim%& ACL is available only when Exim is compiled with DKIM support enabled (which is the default). @@ -25149,7 +25578,6 @@ received, and is executed for each DKIM signature found in a message. If not otherwise specified, the default action is to accept. For details on the operation of DKIM, see chapter &<>&. -.wen .section "The SMTP MIME ACL" "SECID194" @@ -26048,7 +26476,7 @@ warn control = caseful_local_part Notice that we put back the lower cased version afterwards, assuming that is what is wanted for subsequent tests. -.new + .vitem &*control&~=&~debug/*&<&'options'&> .cindex "&ACL;" "enabling debug logging" .cindex "debugging" "enabling from an ACL" @@ -26065,7 +26493,7 @@ contexts): control = debug/opts=+expand+acl control = debug/tag=.$message_exim_id/opts=+expand .endd -.wen + .vitem &*control&~=&~enforce_sync*& &&& &*control&~=&~no_enforce_sync*& @@ -27271,69 +27699,118 @@ rate at which a recipient receives messages, you can use the key &`$local_part@$domain`& with the &%per_rcpt%& option (see below) in a RCPT ACL. -Internally, Exim appends the smoothing constant &'p'& and the options onto the -lookup key because they alter the meaning of the stored data. This is not true -for the limit &'m'&, so you can alter the configured maximum rate and Exim will -still remember clients' past behaviour, but if you alter the other ratelimit -parameters Exim forgets past behaviour. +Each &%ratelimit%& condition can have up to four options. A &%per_*%& option +specifies what Exim measures the rate of, for example messages or recipients +or bytes. You can adjust the measurement using the &%unique=%& and/or +&%count=%& options. You can also control when Exim updates the recorded rate +using a &%strict%&, &%leaky%&, or &%readonly%& option. The options are +separated by a slash, like the other parameters. They may appear in any order. + +Internally, Exim appends the smoothing constant &'p'& onto the lookup key with +any options that alter the meaning of the stored data. The limit &'m'& is not +stored, so you can alter the configured maximum rate and Exim will still +remember clients' past behaviour. If you change the &%per_*%& mode or add or +remove the &%unique=%& option, the lookup key changes so Exim will forget past +behaviour. The lookup key is not affected by changes to the update mode and +the &%count=%& option. -Each &%ratelimit%& condition can have up to three options. One option -specifies what Exim measures the rate of, and the second specifies how Exim -handles excessively fast clients. The third option can be &`noupdate`&, to -disable updating of the ratelimiting database (see section &<>&). -The options are separated by a slash, like the other parameters. They may -appear in any order. .section "Ratelimit options for what is being measured" "ratoptmea" -The &%per_conn%& option limits the client's connection rate. +.cindex "rate limiting" "per_* options" +The &%per_conn%& option limits the client's connection rate. It is not +normally used in the &%acl_not_smtp%&, &%acl_not_smtp_mime%&, or +&%acl_not_smtp_start%& ACLs. The &%per_mail%& option limits the client's rate of sending messages. This is -the default if none of the &%per_*%& options is specified. - -The &%per_byte%& option limits the sender's email bandwidth. Note that it is -best to use this option in the DATA ACL; if it is used in an earlier ACL it -relies on the SIZE parameter specified by the client in its MAIL command, -which may be inaccurate or completely missing. You can follow the limit &'m'& -in the configuration with K, M, or G to specify limits in kilobytes, -megabytes, or gigabytes, respectively. - -The &%per_rcpt%& option causes Exim to limit the rate at which -recipients are accepted. To be effective, it would need to be used in -either the &%acl_smtp_rcpt%& or the &%acl_not_smtp%& ACL. In the -&%acl_smtp_rcpt%& ACL, the number of recipients is incremented by one. -In the case of a locally submitted message in the &%acl_not_smtp%& ACL, -the number of recipients is incremented by the &%$recipients_count%& -for the entire message. Note that in either case the rate limiting -engine will see a message with many recipients as a large high-speed -burst. +the default if none of the &%per_*%& options is specified. It can be used in +&%acl_smtp_mail%&, &%acl_smtp_rcpt%&, &%acl_smtp_predata%&, &%acl_smtp_mime%&, +&%acl_smtp_data%&, or &%acl_not_smtp%&. + +The &%per_byte%& option limits the sender's email bandwidth. It can be used in +the same ACLs as the &%per_mail%& option, though it is best to use this option +in the &%acl_smtp_mime%&, &%acl_smtp_data%& or &%acl_not_smtp%& ACLs; if it is +used in an earlier ACL, Exim relies on the SIZE parameter given by the client +in its MAIL command, which may be inaccurate or completely missing. You can +follow the limit &'m'& in the configuration with K, M, or G to specify limits +in kilobytes, megabytes, or gigabytes, respectively. + +The &%per_rcpt%& option causes Exim to limit the rate at which recipients are +accepted. It can be used in the &%acl_smtp_rcpt%&, &%acl_smtp_predata%&, +&%acl_smtp_mime%&, &%acl_smtp_data%&, or &%acl_smtp_rcpt%& ACLs. In +&%acl_smtp_rcpt%& the rate is updated one recipient at a time; in the other +ACLs the rate is updated with the total recipient count in one go. Note that +in either case the rate limiting engine will see a message with many +recipients as a large high-speed burst. + +The &%per_addr%& option is like the &%per_rcpt%& option, except it counts the +number of different recipients that the client has sent messages to in the +last time period. That is, if the client repeatedly sends messages to the same +recipient, its measured rate is not increased. This option can only be used in +&%acl_smtp_rcpt%&. The &%per_cmd%& option causes Exim to recompute the rate every time the -condition is processed. This can be used to limit the SMTP command rate. -This command is essentially an alias of &%per_rcpt%& to make it clear -that the effect is to limit the rate at which individual commands, -rather than recipients, are accepted. +condition is processed. This can be used to limit the rate of any SMTP +command. If it is used in multiple ACLs it can limit the aggregate rate of +multiple different commands. + +The &%count=%& option can be used to alter how much Exim adds to the client's +measured rate. For example, the &%per_byte%& option is equivalent to +&`per_mail/count=$message_size`&. If there is no &%count=%& option, Exim +increases the measured rate by one (except for the &%per_rcpt%& option in ACLs +other than &%acl_smtp_rcpt%&). The count does not have to be an integer. + +The &%unique=%& option is described in section &<>& below. + + +.section "Ratelimit update modes" "ratoptupd" +.cindex "rate limiting" "reading data without updating" +You can specify one of three options with the &%ratelimit%& condition to +control when its database is updated. This section describes the &%readonly%& +mode, and the next section describes the &%strict%& and &%leaky%& modes. + +If the &%ratelimit%& condition is used in &%readonly%& mode, Exim looks up a +previously-computed rate to check against the limit. + +For example, you can test the client's sending rate and deny it access (when +it is too fast) in the connect ACL. If the client passes this check then it +can go on to send a message, in which case its recorded rate will be updated +in the MAIL ACL. Subsequent connections from the same client will check this +new rate. +.code +acl_check_connect: + deny ratelimit = 100 / 5m / readonly + log_message = RATE CHECK: $sender_rate/$sender_rate_period \ + (max $sender_rate_limit) +# ... +acl_check_mail: + warn ratelimit = 100 / 5m / strict + log_message = RATE UPDATE: $sender_rate/$sender_rate_period \ + (max $sender_rate_limit) +.endd -.section "Ratelimit options for handling fast clients" "ratophanfas" +If Exim encounters multiple &%ratelimit%& conditions with the same key when +processing a message then it may increase the client's measured rate more than +it should. For example, this will happen if you check the &%per_rcpt%& option +in both &%acl_smtp_rcpt%& and &%acl_smtp_data%&. However it's OK to check the +same &%ratelimit%& condition multiple times in the same ACL. You can avoid any +multiple update problems by using the &%readonly%& option on later ratelimit +checks. + +The &%per_*%& options described above do not make sense in some ACLs. If you +use a &%per_*%& option in an ACL where it is not normally permitted then the +update mode defaults to &%readonly%& and you cannot specify the &%strict%& or +&%leaky%& modes. In other ACLs the default update mode is &%leaky%& (see the +next section) so you must specify the &%readonly%& option explicitly. + + +.section "Ratelimit options for handling fast clients" "ratoptfast" +.cindex "rate limiting" "strict and leaky modes" If a client's average rate is greater than the maximum, the rate limiting engine can react in two possible ways, depending on the presence of the -&%strict%& or &%leaky%& options. This is independent of the other +&%strict%& or &%leaky%& update modes. This is independent of the other counter-measures (such as rejecting the message) that may be specified by the -rest of the ACL. The default mode is leaky, which avoids a sender's -over-aggressive retry rate preventing it from getting any email through. +rest of the ACL. -The &%strict%& option means that the client's recorded rate is always -updated. The effect of this is that Exim measures the client's average rate -of attempts to send email, which can be much higher than the maximum it is -actually allowed. If the client is over the limit it may be subjected to -counter-measures by the ACL until it slows down below the maximum rate. If -the client stops attempting to send email for the time specified in the &'p'& -parameter then its computed rate will decay exponentially to 37% of its peak -value. You can work out the time (the number of smoothing periods) that a -client is subjected to counter-measures after an over-limit burst with this -formula: -.code - ln(peakrate/maxrate) -.endd The &%leaky%& (default) option means that the client's recorded rate is not updated if it is above the limit. The effect of this is that Exim measures the client's average rate of successfully sent email, which cannot be greater than @@ -27341,6 +27818,59 @@ the maximum allowed. If the client is over the limit it may suffer some counter-measures (as specified in the ACL), but it will still be able to send email at the configured maximum rate, whatever the rate of its attempts. This is generally the better choice if you have clients that retry automatically. +For example, it does not prevent a sender with an over-aggressive retry rate +from getting any email through. + +The &%strict%& option means that the client's recorded rate is always +updated. The effect of this is that Exim measures the client's average rate +of attempts to send email, which can be much higher than the maximum it is +actually allowed. If the client is over the limit it may be subjected to +counter-measures by the ACL. It must slow down and allow sufficient time to +pass that its computed rate falls below the maximum before it can send email +again. The time (the number of smoothing periods) it must wait and not +attempt to send mail can be calculated with this formula: +.code + ln(peakrate/maxrate) +.endd + + +.section "Limiting the rate of different events" "ratoptuniq" +.cindex "rate limiting" "counting unique events" +The &%ratelimit%& &%unique=%& option controls a mechanism for counting the +rate of different events. For example, the &%per_addr%& option uses this +mechanism to count the number of different recipients that the client has +sent messages to in the last time period; it is equivalent to +&`per_rcpt/unique=$local_part@$domain`&. You could use this feature to +measure the rate that a client uses different sender addresses with the +options &`per_mail/unique=$sender_address`&. + +For each &%ratelimit%& key Exim stores the set of &%unique=%& values that it +has seen for that key. The whole set is thrown away when it is older than the +rate smoothing period &'p'&, so each different event is counted at most once +per period. In the &%leaky%& update mode, an event that causes the client to +go over the limit is not added to the set, in the same way that the client's +recorded rate is not updated in the same situation. + +When you combine the &%unique=%& and &%readonly%& options, the specific +&%unique=%& value is ignored, and Exim just retrieves the client's stored +rate. + +The &%unique=%& mechanism needs more space in the ratelimit database than the +other &%ratelimit%& options in order to store the event set. The number of +unique values is potentially as large as the rate limit, so the extra space +required increases with larger limits. + +The uniqueification is not perfect: there is a small probability that Exim +will think a new event has happened before. If the sender's rate is less than +the limit, Exim should be more than 99.9% correct. However in &%strict%& mode +the measured rate can go above the limit, in which case Exim may under-count +events by a significant margin. Fortunately, if the rate is high enough (2.7 +times the limit) that the false positive rate goes above 9%, then Exim will +throw away the over-full event set before the measured rate falls below the +limit. Therefore the only harm should be that exceptionally high sending rates +are logged incorrectly; any countermeasures you configure will be as effective +as intended. + .section "Using rate limiting" "useratlim" Exim's other ACL facilities are used to define what counter-measures are taken @@ -27384,36 +27914,6 @@ this means that Exim will lose its hints data after a reboot (including retry hints, the callout cache, and ratelimit data). -.section "Reading ratelimit data without updating" "rearatdat" -.cindex "rate limitint" "reading data without updating" -If the &%noupdate%& option is present on a &%ratelimit%& ACL condition, Exim -computes the rate and checks the limit as normal, but it does not update the -saved data. This means that, in relevant ACLs, it is possible to lookup the -existence of a specified (or auto-generated) ratelimit key without incrementing -the ratelimit counter for that key. In order for this to be useful, another ACL -entry must set the rate for the same key (otherwise it will always be zero). -For example: -.code -acl_check_connect: - deny ratelimit = 100 / 5m / strict / per_cmd / noupdate - log_message = RATE: $sender_rate/$sender_rate_period \ - (max $sender_rate_limit) -.endd -.display -&'... some other logic and tests...'& -.endd -.code -acl_check_mail: - warn ratelimit = 100 / 5m / strict / per_cmd - condition = ${if le{$sender_rate}{$sender_rate_limit}} - logwrite = RATE UPDATE: $sender_rate/$sender_rate_period \ - (max $sender_rate_limit) -.endd -In this example, the rate is tested and used to deny access (when it is too -high) in the connect ACL, but the actual computation of the remembered rate -happens later, on a per-command basis, in another ACL. - - .section "Address verification" "SECTaddressverification" .cindex "verifying address" "options for" @@ -27688,7 +28188,7 @@ check for a &"random"& local part at the same domain. The local part is not really random &-- it is defined by the expansion of the option &%callout_random_local_part%&, which defaults to .code -$primary_host_name-$tod_epoch-testing +$primary_hostname-$tod_epoch-testing .endd The idea here is to try to determine whether the remote host accepts all local parts without checking. If it does, there is no point in doing callouts for @@ -28178,7 +28678,7 @@ It supports a &"generic"& interface to scanners called via the shell, and specialized interfaces for &"daemon"& type virus scanners, which are resident in memory and thus are much faster. -.new + .oindex "&%av_scanner%&" You can set the &%av_scanner%& option in first part of the Exim configuration file to specify which scanner to use, together with any additional options that @@ -28192,7 +28692,7 @@ av_scanner = sophie:/var/run/sophie .endd If the value of &%av_scanner%& starts with a dollar character, it is expanded before use. The following scanner types are supported in this release: -.wen + .vlist .vitem &%aveserver%& .cindex "virus scanners" "Kaspersky" @@ -28204,7 +28704,7 @@ example: av_scanner = aveserver:/var/run/aveserver .endd -.new + .vitem &%clamd%& .cindex "virus scanners" "clamd" This daemon-type scanner is GPL and free. You can get it at @@ -28227,7 +28727,7 @@ There is an option WITH_OLD_CLAMAV_STREAM in &_src/EDITME_& available, should you be running a version of ClamAV prior to 0.95. If the option is unset, the default is &_/tmp/clamd_&. Thanks to David Saez for contributing the code for this scanner. -.wen + .vitem &%cmdline%& .cindex "virus scanners" "command line interface" This is the keyword for the generic command line scanner interface. It can be @@ -28364,10 +28864,8 @@ If your virus scanner cannot unpack MIME and TNEF containers itself, you should use the &%demime%& condition (see section &<>&) before the &%malware%& condition. -.new Beware the interaction of Exim's &%message_size_limit%& with any size limits imposed by your anti-virus scanner. -.wen Here is a very simple scanning example: .code @@ -28489,25 +28987,21 @@ SpamAssassin profile has been matched or exceeded. If you want to use the &%spam%& condition for its side effects (see the variables below), you can make it always return &"true"& by appending &`:true`& to the username. -.new .cindex "spam scanning" "returned variables" When the &%spam%& condition is run, it sets up a number of expansion variables. These variables are saved with the received message, thus they are available for use at delivery time. -.wen .vlist .vitem &$spam_score$& The spam score of the message, for example &"3.4"& or &"30.5"&. This is useful for inclusion in log or reject messages. -.new .vitem &$spam_score_int$& The spam score of the message, multiplied by ten, as an integer value. For example &"34"& or &"305"&. It may appear to disagree with &$spam_score$& because &$spam_score$& is rounded and &$spam_score_int$& is truncated. The integer value is useful for numeric comparisons in conditions. -.wen .vitem &$spam_bar$& A string consisting of a number of &"+"& or &"-"& characters, representing the @@ -31194,10 +31688,9 @@ rejected (there seems little point) but instead just get qualified. HELO and EHLO act as RSET; VRFY, EXPN, ETRN and HELP, act as NOOP; QUIT quits. -.new Minimal policy checking is done for BSMTP input. Only the non-SMTP ACL is run in the same way as for non-SMTP local input. -.wen + If an error is detected while reading a message, including a missing &"."& at the end, Exim gives up immediately. It writes details of the error to the standard output in a stylized way that the calling program should be able to @@ -32133,10 +32626,8 @@ log_file_path = $spool_directory/log/%slog If you do not specify anything at build time or run time, that is where the logs are written. -.new A log file path may also contain &`%D`& or &`%M`& if datestamped log file names are in use &-- see section &<>& below. -.wen Here are some examples of possible settings: .display @@ -32176,7 +32667,6 @@ renamed. -.new .section "Datestamped log files" "SECTdatlogfil" .cindex "log" "datestamped files" Instead of cycling the main and reject log files by renaming them @@ -32217,7 +32707,6 @@ log names: /var/spool/exim/log/paniclog /var/log/exim/panic .endd -.wen .section "Logging to syslog" "SECID249" @@ -34050,7 +34539,6 @@ value of the &%-C%& option is identical to the value of CONFIGURE_FILE in &_Local/Makefile_&, Exim ignores &%-C%& and proceeds as usual.) There is no default setting for &%ALT_CONFIG_PREFIX%&. -.new If the permitted configuration files are confined to a directory to which only root has access, this guards against someone who has broken into the Exim account from running a privileged Exim with an arbitrary @@ -34086,7 +34574,6 @@ option, but it cannot be overridden; the runtime option adds additional users to the list. The default setting is &"root"&; this prevents a non-root user who is permitted to modify the runtime file from using Exim as a way to get root. .endlist -.wen @@ -34126,7 +34613,6 @@ abdication; the process cannot regain root afterwards. Prior to release 4.00, After a new Exim process has interpreted its command line options, it changes uid and gid in the following cases: -.new .ilist .oindex "&%-C%&" .oindex "&%-D%&" @@ -34160,7 +34646,7 @@ option). For a daemon, queue runner, delivery, or address testing process, the uid remains as root at this stage, but the gid is changed to the Exim group. .endlist -.wen + The processes that initially retain root privilege behave as follows: .ilist @@ -34395,12 +34881,10 @@ arbitrary program's being run as exim, not as root. -.new .section "Dynamic module directory" "SECTdynmoddir" Any dynamically loadable modules must be installed into the directory defined in &`LOOKUP_MODULE_DIR`& in &_Local/Makefile_& for Exim to permit loading it. -.wen .section "Use of sprintf()" "SECID279" @@ -34759,7 +35243,6 @@ unqualified domain &'foundation'&. Since version 4.70, DKIM support is compiled into Exim by default. It can be disabled by setting DISABLE_DKIM=yes in Local/Makefile. -.new Exim's DKIM implementation allows to .olist Sign outgoing messages: This function is implemented in the SMTP transport. @@ -34769,7 +35252,7 @@ Verify signatures in incoming messages: This is implemented by an additional ACL (acl_smtp_dkim), which can be called several times per message, with different signature contexts. .endlist -.wen + In typical Exim style, the verification implementation does not include any default "policy". Instead it enables you to build your own policy using Exim's standard controls. @@ -34794,7 +35277,6 @@ senders). Signing is implemented by setting private options on the SMTP transport. These options take (expandable) strings as arguments. -.new .option dkim_domain smtp string&!! unset MANDATORY: The domain you want to sign with. The result of this expanded @@ -34844,7 +35326,7 @@ When set, this option must expand to (or be specified as) a colon-separated list of header names. Headers with these names will be included in the message signature. When unspecified, the header names recommended in RFC4871 will be used. -.wen + .section "Verifying DKIM signatures in incoming mail" "SECID514" .cindex "DKIM" "verification" @@ -34862,7 +35344,6 @@ more advanced policies. For that reason, the global option &%dkim_verify_signers%&, and a global expansion variable &%$dkim_signers%& exist. -.new The global 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, @@ -34885,7 +35366,7 @@ You can also be more creative in constructing your policy. For example: .code dkim_verify_signers = $sender_address_domain:$dkim_signers .endd -.wen + 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. @@ -34893,7 +35374,7 @@ If a domain or identity is listed several times in the (expanded) value of Inside the &%acl_smtp_dkim%&, the following expansion variables are available (from most to least important): -.new + .vlist .vitem &%$dkim_cur_signer%& The signer that is being evaluated in this ACL run. This can be a domain or @@ -34967,7 +35448,7 @@ integer size comparisons against this value. A colon-separated list of names of headers included in the signature. .vitem &%$dkim_key_testing%& "1" if the key record has the "testing" flag set, "0" if not. -.vitem &%$dkim_key_nosubdomaining%& +.vitem &%$nosubdomains%& "1" if the key record forbids subdomaining, "0" otherwise. .vitem &%$dkim_key_srvtype%& Service type (tag s=) from the key record. Defaults to "*" if not specified @@ -34978,17 +35459,16 @@ in the key record. .vitem &%$dkim_key_notes%& Notes from the key record (tag n=). .endlist -.wen + In addition, two ACL conditions are provided: -.new .vlist .vitem &%dkim_signers%& ACL condition that checks a colon-separated list of domains or identities for a match against the domain or identity that the ACL is currently verifying (reflected by &%$dkim_cur_signer%&). This is typically used to restrict an ACL verb to a group of domains or identities. For example: -.wen + .code # Warn when message apparently from GMail has no signature at all warn log_message = GMail sender without DKIM signature