-. $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
. the <bookinfo> element must also be updated for each new edition.
. /////////////////////////////////////////////////////////////////////////////
-.set previousversion "4.72"
-.set version "4.73"
+.set previousversion "4.80"
+.set version "4.80"
.set ACL "access control lists (ACLs)"
.set I " "
<bookinfo>
<title>Specification of the Exim Mail Transfer Agent</title>
<titleabbrev>The Exim MTA</titleabbrev>
-<date>29 May 2010</date>
+<date>17 May 2012</date>
<author><firstname>Exim</firstname><surname>Maintainers</surname></author>
<authorinitials>EM</authorinitials>
<revhistory><revision>
- <revnumber>4.73</revnumber>
- <date>19 Nov 2010</date>
+ <revnumber>4.80</revnumber>
+ <date>17 May 2012</date>
<authorinitials>EM</authorinitials>
</revision></revhistory>
-<copyright><year>2009</year><holder>University of Cambridge</holder></copyright>
+<copyright><year>2012</year><holder>University of Cambridge</holder></copyright>
</bookinfo>
.literal off
.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.
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
-
.section "Permanent delivery failure" "SECID21"
.cindex "delivery" "permanent failure"
.cindex "bounce message" "when generated"
to install the PCRE or PCRE development package for your operating
system. If your system has a normal PCRE installation the Exim build
process will need no further configuration. If the library or the
-headers are in an unusual location you will need to set the PCRE_LIBS
-and INCLUDE directives appropriately. If your operating system has no
+headers are in an unusual location you will need to either set the PCRE_LIBS
+and INCLUDE directives appropriately,
+or set PCRE_CONFIG=yes to use the installed &(pcre-config)& command.
+If your operating system has no
PCRE support then you will need to obtain and build the current PCRE
from &url(ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/).
+More information on PCRE is available at &url(http://www.pcre.org/).
.section "DBM libraries" "SECTdb"
.cindex "DBM libraries" "discussion of"
TLS_LIBS=-L/usr/local/openssl/lib -lssl -lcrypto
TLS_INCLUDE=-I/usr/local/openssl/include/
.endd
+.cindex "pkg-config" "OpenSSL"
+If you have &'pkg-config'& available, then instead you can just use:
+.code
+SUPPORT_TLS=yes
+USE_OPENSSL_PC=openssl
+.endd
.cindex "USE_GNUTLS"
If GnuTLS is installed, you should set
.code
TLS_LIBS=-L/usr/gnu/lib -lgnutls -ltasn1 -lgcrypt
TLS_INCLUDE=-I/usr/gnu/include
.endd
+.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
+
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 &<<CHAPTLS>>&.
.section "Use of tcpwrappers" "SECID27"
-.new
+
.cindex "tcpwrappers, building Exim to support"
.cindex "USE_TCP_WRAPPERS"
.cindex "TCP_WRAPPERS_DAEMON_NAME"
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"
+.section "Dynamically loaded lookup module support" "SECTdynamicmodules"
+.cindex "lookup modules"
+.cindex "dynamic modules"
+.cindex ".so building"
+On some platforms, Exim supports not compiling all lookup types directly into
+the main binary, instead putting some into external modules which can be loaded
+on demand.
+This permits packagers to build Exim with support for lookups with extensive
+library dependencies without requiring all users to install all of those
+dependencies.
+Most, but not all, lookup types can be built this way.
+
+Set &`LOOKUP_MODULE_DIR`& to the directory into which the modules will be
+installed; Exim will only load modules from that directory, as a security
+measure. You will need to set &`CFLAGS_DYNAMIC`& if not already defined
+for your OS; see &_OS/Makefile-Linux_& for an example.
+Some other requirements for adjusting &`EXTRALIBS`& may also be necessary,
+see &_src/EDITME_& for details.
+
+Then, for each module to be loaded dynamically, define the relevant
+&`LOOKUP_`&<&'lookup_type'&> flags to have the value "2" instead of "yes".
+For example, this will build in lsearch but load sqlite and mysql support
+on demand:
+.code
+LOOKUP_LSEARCH=yes
+LOOKUP_SQLITE=2
+LOOKUP_MYSQL=2
+.endd
+
+
.section "The building process" "SECID29"
.cindex "build directory"
Once &_Local/Makefile_& (and &_Local/eximon.conf_&, if required) have been
binary, attempts to configure Exim to use it cause run time configuration
errors.
+.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
+
.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,
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%&"
if this is required. If the &%bi_command%& option is not set, calling Exim with
&%-bi%& is a no-op.
+.new
+. // Keep :help first, then the rest in alphabetical order
+.vitem &%-bI:help%&
+.oindex "&%-bI:help%&"
+.cindex "querying exim information"
+We shall provide various options starting &`-bI:`& for querying Exim for
+information. The output of many of these will be intended for machine
+consumption. This one is not. The &%-bI:help%& option asks Exim for a
+synopsis of supported options beginning &`-bI:`&. Use of any of these
+options shall cause Exim to exit after producing the requested output.
+
+.vitem &%-bI:dscp%&
+.oindex "&%-bI:dscp%&"
+.cindex "DSCP" "values"
+This option causes Exim to emit an alphabetically sorted list of all
+recognised DSCP names.
+
+.vitem &%-bI:sieve%&
+.oindex "&%-bI:sieve%&"
+.cindex "Sieve filter" "capabilities"
+This option causes Exim to emit an alphabetically sorted list of all supported
+Sieve protocol extensions on stdout, one per line. This is anticipated to be
+useful for ManageSieve (RFC 5804) implementations, in providing that protocol's
+&`SIEVE`& capability response line. As the precise list may depend upon
+compile-time build options, which this option will adapt to, this is the only
+way to guarantee a correct response.
+.wen
+
.vitem &%-bm%&
.oindex "&%-bm%&"
.cindex "local message reception"
preference to the address taken from the message. The caller of Exim must be a
trusted user for the sender of a message to be set in this way.
+.vitem &%-bmalware%&&~<&'filename'&>
+.oindex "&%-bmalware%&"
+.cindex "testing", "malware"
+.cindex "malware scan test"
+This debugging option causes Exim to scan the given file,
+using the malware scanning framework. The option of &%av_scanner%& influences
+this option, so if &%av_scanner%&'s value is dependent upon an expansion then
+the expansion should have defaults which apply to this invocation. ACLs are
+not invoked, so if &%av_scanner%& references an ACL variable then that variable
+will never be populated and &%-bmalware%& will fail.
+
+Exim will have changed working directory before resolving the filename, so
+using fully qualified pathnames is advisable. Exim will be running as the Exim
+user when it tries to open the file, rather than as the invoking user.
+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.
+
.vitem &%-bnq%&
.oindex "&%-bnq%&"
.cindex "address qualification, suppressing"
If a list of configuration files was supplied, the value that is output here
is the name of the file that was actually used.
+.new
+.cindex "options" "hiding name of"
+If the &%-n%& flag is given, then for most modes of &%-bP%& operation the
+name will not be output.
+.wen
+
.cindex "daemon" "process id (pid)"
.cindex "pid (process id)" "of daemon"
If &%log_file_path%& or &%pid_file_path%& are given, the names of the
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"
-.cindex "malware scan test"
-This debugging option causes Exim to scan the given file,
-using the malware scanning framework. The option of &%av_scanner%& influences
-this option, so if &%av_scanner%&'s value is dependent upon an expansion then
-the expansion should have defaults which apply to this invocation. ACLs are
-not invoked, so if &%av_scanner%& references an ACL variable then that variable
-will never be populated and &%-bmalware%& will fail.
-
-Exim will have changed working directory before resolving the filename, so
-using fully qualified pathnames is advisable. Exim will be running as the Exim
-user when it tries to open the file, rather than as the invoking user.
-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%&"
.cindex "testing" "addresses"
than a recipient address. This affects any rewriting and qualification that
might happen.
-.new
+.vitem &%-bw%&
+.oindex "&%-bw%&"
+.cindex "daemon"
+.cindex "inetd"
+.cindex "inetd" "wait mode"
+This option runs Exim as a daemon, awaiting incoming SMTP connections,
+similarly to the &%-bd%& option. All port specifications on the command-line
+and in the configuration file are ignored. Queue-running may not be specified.
+
+In this mode, Exim expects to be passed a socket as fd 0 (stdin) which is
+listening for connections. This permits the system to start up and have
+inetd (or equivalent) listen on the SMTP ports, starting an Exim daemon for
+each port only when the first connection is received.
+
+If the option is given as &%-bw%&<&'time'&> then the time is a timeout, after
+which the daemon will exit, which should cause inetd to listen once more.
+
.vitem &%-C%&&~<&'filelist'&>
.oindex "&%-C%&"
.cindex "configuration file" "alternate"
caller is privileged, or unless it is an exotic configuration that does not
require privilege. No check is made on the owner or group of the files
specified by this option.
-.wen
-.new
+
.vitem &%-D%&<&'macro'&>=<&'value'&>
.oindex "&%-D%&"
.cindex "macro" "setting on command line"
exim '-D ABC = something' ...
.endd
&%-D%& may be repeated up to 10 times on a command line.
-.wen
+
.vitem &%-d%&<&'debug&~options'&>
.oindex "&%-d%&"
.vitem &%-n%&
.oindex "&%-n%&"
-.cindex "Sendmail compatibility" "&%-n%& option ignored"
-This option is interpreted by Sendmail to mean &"no aliasing"&. It is ignored
-by Exim.
+This option is interpreted by Sendmail to mean &"no aliasing"&.
+For normal modes of operation, it is ignored by Exim.
+When combined with &%-bP%& it suppresses the name of an option from being output.
.vitem &%-O%&&~<&'data'&>
.oindex "&%-O%&"
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"
CONFIGURE_FILE is a list, no default is automatically installed. Chapter
&<<CHAPdefconfil>>& is a &"walk-through"& discussion of the default
configuration.
-.wen
+
.section "Using a different configuration file" "SECID40"
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.
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.
i.e. PLAIN or LOGIN. The &%server_advertise_condition%& setting controls
when Exim offers authentication to clients; in the examples, this is only
when TLS or SSL has been started, so to enable the authenticators you also
-need to add support for TLS as described in &<<SECTdefconfmain>>&.
+need to add support for TLS as described in section &<<SECTdefconfmain>>&.
The &%server_condition%& setting defines how to verify that the username and
password are correct. In the examples it just produces an error message.
To make the authenticators work, you can use a string expansion
-expression like one of the examples in &<<CHAPplaintext>>&.
+expression like one of the examples in chapter &<<CHAPplaintext>>&.
Beware that the sequence of the parameters to PLAIN and LOGIN differ; the
-usercode and password are in different positions. &<<CHAPplaintext>>&
-covers both.
+usercode and password are in different positions.
+Chapter &<<CHAPplaintext>>& covers both.
.ecindex IIDconfiwal
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.)
.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.
+.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
&`fail`& keyword causes a &'forced expansion failure'& &-- see section
&<<SECTforexpfai>>& for an explanation of what this means.
-The supported DNS record types are A, CNAME, MX, NS, PTR, SRV, and TXT, and,
-when Exim is compiled with IPv6 support, AAAA (and A6 if that is also
+The supported DNS record types are A, CNAME, MX, NS, PTR, SPF, SRV, and TXT,
+and, when Exim is compiled with IPv6 support, AAAA (and A6 if that is also
configured). If no type is given, TXT is assumed. When the type is PTR,
the data can be an IP address, written as normal; inversion and the addition of
&%in-addr.arpa%& or &%ip6.arpa%& happens automatically. For example:
white space is ignored.
.cindex "TXT record" "in &(dnsdb)& lookup"
+.cindex "SPF record" "in &(dnsdb)& lookup"
For TXT records with multiple items of data, only the first item is returned,
unless a separator for them is specified using a comma after the separator
character followed immediately by the TXT record item separator. To concatenate
-items without a separator, use a semicolon instead.
+items without a separator, use a semicolon instead. For SPF records the
+default behaviour is to concatenate multiple items without using a separator.
.code
${lookup dnsdb{>\n,: txt=a.b.example}}
${lookup dnsdb{>\n; txt=a.b.example}}
+${lookup dnsdb{spf=example.org}}
.endd
It is permitted to specify a space as the separator character. Further
white space is ignored.
secure (encrypted) LDAP connections. The second of these ensures that an
encrypted TLS connection is used.
+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.
+
.section "LDAP quoting" "SECID68"
.cindex "LDAP" "quoting"
chapter &<<CHAPfdlookup>>&. For example:
.code
hold_domains = mysql;select domain from holdlist \
- where domain = '$domain';
+ where domain = '${quote_mysql:$domain}';
.endd
In most cases, the data that is looked up is not used (so for an SQL query, for
example, it doesn't matter what field you select). Exim is interested only in
below in section &<<SECTexpansionitems>>& onwards. Backslash is used as an
escape character, as described in the following section.
+Whether a string is expanded depends upon the context. Usually this is solely
+dependent upon the option for which a value is sought; in this documentation,
+options for which string expansion is performed are marked with † after
+the data type. ACL rules always expand strings. A couple of expansion
+conditions do not expand some of the brace-delimited branches, for security
+reasons.
+
.section "Literal text in expanded strings" "SECTlittext"
permitted. This can be useful when processing numbers extracted from dates or
times, which often do have leading zeros.
-A number may be followed by &"K"& or &"M"& to multiply it by 1024 or 1024*1024,
+A number may be followed by &"K"&, &"M"& or &"G"& to multiply it by 1024, 1024*1024
+or 1024*1024*1024,
respectively. Negative numbers are supported. The result of the computation is
-a decimal representation of the answer (without &"K"& or &"M"&). For example:
+a decimal representation of the answer (without &"K"&, &"M"& or &"G"&). For example:
.display
&`${eval:1+1} `& yields 2
supplied number and is at least 0. The quality of this randomness depends
on how Exim was built; the values are not suitable for keying material.
If Exim is linked against OpenSSL then RAND_pseudo_bytes() is used.
+If Exim is linked against GnuTLS then gnutls_rnd(GNUTLS_RND_NONCE) is used,
+for versions of GnuTLS with that function.
Otherwise, the implementation may be arc4random(), random() seeded by
srandomdev() or srandom(), or a custom implementation even weaker than
random().
-.new
.vitem &*${reverse_ip:*&<&'ipaddr'&>&*}*&
.cindex "expansion" "IP address"
This operator reverses an IP address; for IPv4 addresses, the result is in
dotted-nibble hexadecimal form. In both cases, this is the "natural" form
for DNS. For example,
.code
-${reverse_ip:192.0.2.4} and ${reverse_ip:2001:0db8:c42:9:1:abcd:192.0.2.3}
+${reverse_ip:192.0.2.4}
+${reverse_ip:2001:0db8:c42:9:1:abcd:192.0.2.3}
.endd
returns
.code
-4.2.0.192 and 3.0.2.0.0.0.0.c.d.c.b.a.1.0.0.0.9.0.0.0.2.4.c.0.8.b.d.0.1.0.0.2
+4.2.0.192
+3.0.2.0.0.0.0.c.d.c.b.a.1.0.0.0.9.0.0.0.2.4.c.0.8.b.d.0.1.0.0.2
.endd
-.wen
.vitem &*${rfc2047:*&<&'string'&>&*}*&
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
.code
${if bool{$acl_m_privileged_sender} ...
.endd
-.wen
.vitem &*bool_lax&~{*&<&'string'&>&*}*&
includes the case of letters, whereas for &%gti%& the comparison is
case-independent.
+.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
+
.vitem &*isip&~{*&<&'string'&>&*}*& &&&
&*isip4&~{*&<&'string'&>&*}*& &&&
&*isip6&~{*&<&'string'&>&*}*&
.cindex "&%match_ip%& expansion condition"
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:
.code
${if match_ip{$sender_host_address}{1.2.3.4:5.6.7.8}{...}{...}}
.endd
.endlist ilist
+Note that <&'string2'&> is not itself subject to string expansion, unless
+Exim was built with the EXPAND_LISTMATCH_RHS option.
+
Consult section &<<SECThoslispatip>>& for further details of these patterns.
.vitem &*match_local_part&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*&
have their local parts matched casefully. Domains are always matched
caselessly.
+Note that <&'string2'&> is not itself subject to string expansion, unless
+Exim was built with the EXPAND_LISTMATCH_RHS option.
+
&*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
negative response to an AUTH command, including (for example) an attempt to use
an undefined mechanism.
+.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.
+
.vitem &$body_linecount$&
.cindex "message body" "line count"
.cindex "body of message" "line count"
.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 "&$bounce_recipient$&"
routers, and transports run) the count is increased to include the
&'Received:'& header line that Exim standardly adds, and also any other header
lines that are added by ACLs. The blank line that separates the message header
-from the body is not counted. Here is an example of the use of this variable in
-a DATA ACL:
+from the body is not counted.
+
+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).
+
+Here is an example of the use of this variable in a DATA ACL:
.code
deny message = Too many lines in message header
condition = \
received. It is empty if there was no successful authentication. See also
&$authenticated_id$&.
+.new
+.vitem &$sender_host_dnssec$&
+.vindex "&$sender_host_dnssec$&"
+If &$sender_host_name$& has been populated (by reference, &%hosts_lookup%& or
+otherwise) then this boolean will have been set true if, and only if, the
+resolver library states that the reverse DNS was authenticated data. At all
+other times, this variable is false.
+
+It is likely that you will need to coerce DNSSEC support on in the resolver
+library, by setting:
+.code
+dns_use_dnssec = 1
+.endd
+
+Exim does not perform DNSSEC validation itself, instead leaving that to a
+validating resolver (eg, unbound, or bind with suitable configuration).
+
+Exim does not (currently) check to see if the forward DNS was also secured
+with DNSSEC, only the reverse DNS.
+
+If you have changed &%host_lookup_order%& so that &`bydns`& is not the first
+mechanism in the list, then this variable will be false.
+.wen
+
+
.vitem &$sender_host_name$&
.vindex "&$sender_host_name$&"
When a message is received from a remote host, this variable contains the
command, which can be found in the separate document entitled &'Exim's
interfaces to mail filtering'&.
+.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).
+
.vitem &$tls_certificate_verified$&
.vindex "&$tls_certificate_verified$&"
This variable is set to &"1"& if a TLS certificate was verified when the
value is retained during message delivery, except during outbound SMTP
deliveries.
+.vitem &$tls_sni$&
+.vindex "&$tls_sni$&"
+.cindex "TLS" "Server Name Indication"
+When a TLS session is being established, if the client sends the Server
+Name Indication extension, the value will be placed in this variable.
+If the variable appears in &%tls_certificate%& then this option and
+some others, described in &<<SECTtlssni>>&,
+will be re-expanded early in the TLS session, to permit
+a different certificate to be presented (and optionally a different key to be
+used) to the client, based upon the value of the SNI extension.
+
+The value will be retained for the lifetime of the message. During outbound
+SMTP deliveries, it reflects the value of the &%tls_sni%& option on
+the transport.
+
.vitem &$tod_bsdinbox$&
.vindex "&$tod_bsdinbox$&"
The time of day and the date, in the format required for BSD-style mailbox
.vindex "&$tod_epoch$&"
The time and date as a number of seconds since the start of the Unix epoch.
+.vitem &$tod_epoch_l$&
+.vindex "&$tod_epoch_l$&"
+The time and date as a number of microseconds since the start of the Unix epoch.
+
.vitem &$tod_full$&
.vindex "&$tod_full$&"
A full version of the time and date, for example: Wed, 16 Oct 1995 09:51:40
.section "Data lookups" "SECID101"
.table2
.row &%ibase_servers%& "InterBase servers"
+.row &%ldap_ca_cert_dir%& "dir of CA certs to verify LDAP server's"
+.row &%ldap_ca_cert_file%& "file of CA certs to verify LDAP server's"
+.row &%ldap_cert_file%& "client cert file for LDAP"
+.row &%ldap_cert_key%& "client key file for LDAP"
+.row &%ldap_cipher_suite%& "TLS negotiation preference control"
.row &%ldap_default_servers%& "used if no server in query"
+.row &%ldap_require_cert%& "action to take without LDAP server cert"
+.row &%ldap_start_tls%& "require TLS within LDAP"
.row &%ldap_version%& "set protocol version"
.row &%lookup_open_max%& "lookup files held open"
.row &%mysql_servers%& "default MySQL servers"
.section "TLS" "SECID108"
.table2
-.row &%gnutls_require_kx%& "control GnuTLS key exchanges"
-.row &%gnutls_require_mac%& "control GnuTLS MAC algorithms"
-.row &%gnutls_require_protocols%& "control GnuTLS protocols"
.row &%gnutls_compat_mode%& "use GnuTLS compatibility mode"
.row &%openssl_options%& "adjust OpenSSL compatibility options"
.row &%tls_advertise_hosts%& "advertise TLS to these hosts"
.row &%tls_certificate%& "location of server certificate"
.row &%tls_crl%& "certificate revocation list"
+.row &%tls_dh_max_bits%& "clamp D-H bit count suggestion"
.row &%tls_dhparam%& "DH parameters for server"
.row &%tls_on_connect_ports%& "specify SSMTP (SMTPS) ports"
.row &%tls_privatekey%& "location of server private key"
.row &%dns_ipv4_lookup%& "only v4 lookup for these domains"
.row &%dns_retrans%& "parameter for resolver"
.row &%dns_retry%& "parameter for resolver"
+.new
+.row &%dns_use_dnssec%& "parameter for resolver"
+.wen
+.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"
Those options that undergo string expansion before use are marked with
†.
-.option accept_8bitmime main boolean false
+.option accept_8bitmime main boolean true
.cindex "8BITMIME"
.cindex "8-bit characters"
This option causes Exim to send 8BITMIME in its response to an SMTP
EHLO command, and to accept the BODY= parameter on MAIL commands.
However, though Exim is 8-bit clean, it is not a protocol converter, and it
takes no steps to do anything special with messages received by this route.
-Consequently, this option is turned off by default.
+
+Historically Exim kept this option off by default, but the maintainers
+feel that in today's Internet, this causes more problems than it solves.
+It now defaults to true.
+A more detailed analysis of the issues is provided by Dan Bernstein:
+.display
+&url(http://cr.yp.to/smtp/8bitmime.html)
+.endd
.option acl_not_smtp main string&!! unset
.cindex "&ACL;" "for non-SMTP messages"
&%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.
+
.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:
before use. See section &<<SECTscanvirus>>& for further details.
-
.option bi_command main string unset
.oindex "&%-bi%&"
This option supplies the name of a command that is run when Exim is called with
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 &<<CALLaddparcall>>& for details of how this value is used.
See &%dns_retrans%& above.
+.new
+.option dns_use_dnssec main integer -1
+.cindex "DNS" "resolver options"
+.cindex "DNS" "DNSSEC"
+If this option is set to a non-negative number then Exim will initialise the
+DNS resolver library to either use or not use DNSSEC, overriding the system
+default. A value of 0 coerces DNSSEC off, a value of 1 coerces DNSSEC on.
+
+If the resolver library does not support DNSSEC then this option has no effect.
+.wen
+
+
+.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.
+
+
.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
See &%gecos_name%& above.
-.option gnutls_require_kx main string unset
-This option controls the key exchange mechanisms when GnuTLS is used in an Exim
-server. For details, see section &<<SECTreqciphgnu>>&.
-
-.option gnutls_require_mac main string unset
-This option controls the MAC algorithms when GnuTLS is used in an Exim
-server. For details, see section &<<SECTreqciphgnu>>&.
-
-.option gnutls_require_protocols main string unset
-This option controls the protocols when GnuTLS is used in an Exim
-server. For details, see section &<<SECTreqciphgnu>>&.
-
.option gnutls_compat_mode main boolean unset
This option controls whether GnuTLS is used in compatibility mode in an Exim
server. This reduces security slightly, but improves interworking with older
logged.
+.option ldap_ca_cert_dir main string unset
+.cindex "LDAP", "TLS CA certificate directory"
+This option indicates which directory contains CA certificates for verifying
+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.
+
+
+.option ldap_ca_cert_file main string unset
+.cindex "LDAP", "TLS CA certificate file"
+This option indicates which file contains CA certificates for verifying
+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.
+
+
+.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%&.
+
+
+.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.
+
+
+.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 &<<SECTreqciphssl>>& for more details of the format of
+cipher-suite options with OpenSSL (as used by LDAP client libraries).
+
+
.option ldap_default_servers main "string list" unset
.cindex "LDAP" "default servers"
This option provides a list of LDAP servers which are tried in turn when an
with LDAP support.
+.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".
+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.
+
+
+.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
+connecting on a regular LDAP port. This is the LDAP equivalent of SMTP's
+"STARTTLS". This is distinct from using "ldaps", which is the LDAP form
+of SSL-on-connect.
+In the event of failure to negotiate TLS, the action taken is controlled
+by &%ldap_require_cert%&.
+
+
.option ldap_version main integer unset
.cindex "LDAP" "protocol version, forcing"
This option can be used to force Exim to set a specific protocol version for
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
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
transport driver.
-.new
-.option openssl_options main "string list" +dont_insert_empty_fragments
+.option openssl_options main "string list" "+no_sslv2"
.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
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.
+
+Historical note: prior to release 4.80, 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.
An example:
.code
-openssl_options = -all +microsoft_big_sslv3_buffer
+# Make both old MS and old Eudora happy:
+openssl_options = -all +microsoft_big_sslv3_buffer \
+ +dont_insert_empty_fragments
.endd
-.wen
+
+Possible options may include:
+.ilist
+&`all`&
+.next
+&`allow_unsafe_legacy_renegotiation`&
+.next
+&`cipher_server_preference`&
+.next
+&`dont_insert_empty_fragments`&
+.next
+&`ephemeral_rsa`&
+.next
+&`legacy_server_connect`&
+.next
+&`microsoft_big_sslv3_buffer`&
+.next
+&`microsoft_sess_id_bug`&
+.next
+&`msie_sslv2_rsa_padding`&
+.next
+&`netscape_challenge_bug`&
+.next
+&`netscape_reuse_cipher_change_bug`&
+.next
+&`no_compression`&
+.next
+&`no_session_resumption_on_renegotiation`&
+.next
+&`no_sslv2`&
+.next
+&`no_sslv3`&
+.next
+&`no_ticket`&
+.next
+&`no_tlsv1`&
+.next
+&`no_tlsv1_1`&
+.next
+&`no_tlsv1_2`&
+.next
+&`single_dh_use`&
+.next
+&`single_ecdh_use`&
+.next
+&`ssleay_080_client_dh_bug`&
+.next
+&`sslref2_reuse_cert_type_bug`&
+.next
+&`tls_block_padding_bug`&
+.next
+&`tls_d5_bug`&
+.next
+&`tls_rollback_bug`&
+.endlist
.option oracle_servers main "string list" unset
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
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
use when sending messages as a client, you must set the &%tls_certificate%&
option in the relevant &(smtp)& transport.
+If the option contains &$tls_sni$& and Exim is built against OpenSSL, then
+if the OpenSSL build supports TLS extensions and the TLS client sends the
+Server Name Indication extension, then this option and others documented in
+&<<SECTtlssni>>& will be re-expanded.
.option tls_crl main string&!! unset
.cindex "TLS" "server certificate revocation list"
This option specifies a certificate revocation list. The expanded value must
be the name of a file that contains a CRL in PEM format.
+See &<<SECTtlssni>>& for discussion of when this option might be re-expanded.
+
+
+.option tls_dh_max_bits main integer 2236
+.cindex "TLS" "D-H bit count"
+The number of bits used for Diffie-Hellman key-exchange may be suggested by
+the chosen TLS library. That value might prove to be too high for
+interoperability. This option provides a maximum clamp on the value
+suggested, trading off security for interoperability.
+
+The value must be at least 1024.
+
+The value 2236 was chosen because, at time of adding the option, it was the
+hard-coded maximum value supported by the NSS cryptographic library, as used
+by Thunderbird, while GnuTLS was suggesting 2432 bits as normal.
+
+If you prefer more security and are willing to break some clients, raise this
+number.
+
+Note that the value passed to GnuTLS for *generating* a new prime may be a
+little less than this figure, because GnuTLS is inexact and may produce a
+larger prime than requested.
+
.option tls_dhparam main string&!! unset
.cindex "TLS" "D-H parameters for server"
-The value of this option is expanded, and must then be the absolute path to
-a file which contains the server's DH parameter values.
-This is used only for OpenSSL. When Exim is linked with GnuTLS, this option is
-ignored. See section &<<SECTopenvsgnu>>& for further details.
+The value of this option is expanded and indicates the source of DH parameters
+to be used by Exim.
+
+If it is a filename starting with a &`/`&, then it names a file from which DH
+parameters should be loaded. If the file exists, it should hold a PEM-encoded
+PKCS#3 representation of the DH prime. If the file does not exist, for
+OpenSSL it is an error. For GnuTLS, Exim will attempt to create the file and
+fill it with a generated DH prime. For OpenSSL, if the DH bit-count from
+loading the file is greater than &%tls_dh_max_bits%& then it will be ignored,
+and treated as though the &%tls_dhparam%& were set to "none".
+
+If this option expands to the string "none", then no DH parameters will be
+loaded by Exim.
+
+If this option expands to the string "historic" and Exim is using GnuTLS, then
+Exim will attempt to load a file from inside the spool directory. If the file
+does not exist, Exim will attempt to create it.
+See section &<<SECTgnutlsparam>>& for further details.
+
+If Exim is using OpenSSL and this option is empty or unset, then Exim will load
+a default DH prime; the default is the 2048 bit prime described in section
+2.2 of RFC 5114, "2048-bit MODP Group with 224-bit Prime Order Subgroup", which
+in IKE is assigned number 23.
+
+Otherwise, the option must expand to the name used by Exim for any of a number
+of DH primes specified in RFC 2409, RFC 3526 and RFC 5114. As names, Exim uses
+"ike" followed by the number used by IKE, of "default" which corresponds to
+"ike23".
+
+The available primes are:
+&`ike1`&, &`ike2`&, &`ike5`&,
+&`ike14`&, &`ike15`&, &`ike16`&, &`ike17`&, &`ike18`&,
+&`ike22`&, &`ike23`& (aka &`default`&) and &`ike24`&.
+
+Some of these will be too small to be accepted by clients.
+Some may be too large to be accepted by clients.
.option tls_on_connect_ports main "string list" unset
key is assumed to be in the same file as the server's certificates. See chapter
&<<CHAPTLS>>& for further details.
+See &<<SECTtlssni>>& for discussion of when this option might be re-expanded.
+
.option tls_remember_esmtp main boolean false
.cindex "TLS" "esmtp state; remembering"
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.
+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.
+
+See &<<SECTtlssni>>& for discussion of when this option might be re-expanded.
+
.option tls_verify_hosts main "host list&!!" unset
.cindex "TLS" "client certificate verification"
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
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,
.code
condition = ${if >{$message_age}{600}{true}{}}
.endd
-.new
+
A multiple condition example, which succeeds:
.code
condition = ${if >{$message_age}{600}}
condition = ${if !eq{${lc:$local_part}}{postmaster}}
condition = foobar
.endd
-.wen
+
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%&.
-
.option debug_print routers string&!! unset
.cindex "testing" "variables in drivers"
If this option is set and debugging is enabled (see the &%-d%& command line
case routing fails.
+.section "Declining addresses by dnslookup" "SECTdnslookupdecline"
+.cindex "&(dnslookup)& router" "declines"
+There are a few cases where a &(dnslookup)& router will decline to accept
+an address; if such a router is expected to handle "all remaining non-local
+domains", then it is important to set &%no_more%&.
+
+Reasons for a &(dnslookup)& router to decline currently include:
+.ilist
+The domain does not exist in DNS
+.next
+The domain exists but the MX record's host part is just "."; this is a common
+convention (borrowed from SRV) used to indicate that there is no such service
+for this domain and to not fall back to trying A/AAAA records.
+.next
+Ditto, but for SRV records, when &%check_srv%& is set on this router.
+.next
+MX record points to a non-existent host.
+.next
+MX record points to an IP address and the main section option
+&%allow_mx_to_ip%& is not set.
+.next
+MX records exist and point to valid hosts, but all hosts resolve only to
+addresses blocked by the &%ignore_target_hosts%& generic option on this router.
+.next
+The domain is not syntactically valid (see also &%allow_utf8_domains%& and
+&%dns_check_names_pattern%& for handling one variant of this)
+.next
+&%check_secondary_mx%& is set on this router but the local host can
+not be found in the MX records (see below)
+.endlist
+
+
.section "Private options for dnslookup" "SECID118"
.endd
is interpreted as a pipe with a rather strange command name, and no arguments.
+.new
+Note that the above example assumes that the text comes from a lookup source
+of some sort, so that the quotes are part of the data. If composing a
+redirect router with a &%data%& option directly specifying this command, the
+quotes will be used by the configuration parser to define the extent of one
+string, but will not be passed down into the redirect router itself. There
+are two main approaches to get around this: escape quotes to be part of the
+data itself, or avoid using this mechanism and instead create a custom
+transport with the &%command%& option set and reference that transport from
+an &%accept%& router.
+.wen
+
.next
.cindex "file" "in redirection list"
.cindex "address redirection" "to file"
section &<<SECTmaildirdelivery>>& below.
-.option maildir_use_size_file appendfile boolean false
+.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
file name (even though &%maildir_tag%& puts it there) because maildir MUAs
sometimes add other information onto the ends of message file names.
+Section &<<SECID136>>& contains further information.
.option quota_warn_message appendfile string&!! "see below"
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.
+
.vindex "&$message_size$&"
Tags can be used to encode the size of files in their names; see
&%quota_size_regex%& above for an example. The expansion of &%maildir_tag%&
be deferred. The expanded tag may contain any printing characters except &"/"&.
Non-printing characters in the string are ignored; if the resulting string is
empty, it is ignored. If it starts with an alphanumeric character, a leading
-colon is inserted.
+colon is inserted; this default has not proven to be the path that popular
+maildir implementations have chosen (but changing it in Exim would break
+backwards compatibility).
+For one common implementation, you might set:
+.code
+maildir_tag = ,S=${message_size}
+.endd
+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.
.section "Using a maildirsize file" "SECID136"
logged, but are not included in the bounce message, which merely contains
&"local delivery failed"&.
+If the command exits on a signal and the &%freeze_signal%& option is set then
+the message will be frozen in the queue. If that option is not set, a bounce
+will be sent as normal.
+
If the return code is greater than 128 and the command being run is a shell
script, it normally means that the script was terminated by a signal whose
-value is the return code minus 128.
+value is the return code minus 128. The &%freeze_signal%& option does not
+apply in this case.
If Exim is unable to run the command (that is, if &[execve()]& fails), the
return code is set to 127. This is the value that a shell returns if it is
frozen, whatever the setting of &%ignore_status%&.
+.option freeze_signal pipe boolean false
+.cindex "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.
+
+
.option ignore_status pipe boolean false
If this option is true, the status returned by the subprocess that is set up to
run the command is ignored, and Exim behaves as if zero had been returned.
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
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
.section "Use of $tls_cipher and $tls_peerdn" "usecippeer"
+.vindex &$tls_bits$&
.vindex &$tls_cipher$&
.vindex &$tls_peerdn$&
-At the start of a run of the &(smtp)& transport, the values of &$tls_cipher$&
-and &$tls_peerdn$& are the values that were set when the message was received.
+.vindex &$tls_sni$&
+At the start of a run of the &(smtp)& transport, the values of &$tls_bits$&,
+&$tls_cipher$&, &$tls_peerdn$& and &$tls_sni$&
+are the values that were set when the message was received.
These are the values that are used for options that are expanded before any
-SMTP connections are made. Just before each connection is made, these two
+SMTP connections are made. Just before each connection is made, these four
variables are emptied. If TLS is subsequently started, they are set to the
appropriate values for the outgoing connection, and these are the values that
are in force when any authenticators are run and when the
details.
+.new
+.option dscp smtp string&!! unset
+.cindex "DCSP"
+.cindex "DiffServ"
+This option causes the DSCP value associated with a socket to be set to one
+of a number of fixed strings or to numeric value.
+The &%-bI:dscp%& option may be used to ask Exim which names it knows of.
+Common values include &`throughput`&, &`mincost`&, and on newer systems
+&`ef`&, &`af41`&, etc. Numeric values may be in the range 0 to 0x3F.
+
+The outbound packets from Exim will be marked with this value in the header
+(for IPv4, the TOS field; for IPv6, the TCLASS field); there is no guarantee
+that these packets will have any effect, not be stripped by networking
+equipment, or do much of anything without cooperation with your Network
+Engineer and those of all network operators between the source and destination.
+.wen
+
.option fallback_hosts smtp "string list" unset
.cindex "fallback" "hosts specified on transport"
instead of using the DNS. Of course, that function may in fact use the DNS, but
it may also consult other sources of information such as &_/etc/hosts_&.
-.option gnutls_require_kx smtp string unset
-This option controls the key exchange mechanisms when GnuTLS is used in an Exim
-client. For details, see section &<<SECTreqciphgnu>>&.
-
-.option gnutls_require_mac smtp string unset
-This option controls the MAC algorithms when GnuTLS is used in an Exim
-client. For details, see section &<<SECTreqciphgnu>>&.
-
-.option gnutls_require_protocols smtp string unset
-This option controls the protocols when GnuTLS is used in an Exim
-client. For details, see section &<<SECTreqciphgnu>>&.
-
.option gnutls_compat_mode smtp boolean unset
This option controls whether GnuTLS is used in compatibility mode in an Exim
server. This reduces security slightly, but improves interworking with older
.option protocol smtp string smtp
.cindex "LMTP" "over TCP/IP"
+.cindex "ssmtp protocol" "outbound"
+.cindex "TLS" "SSL-on-connect outbound"
+.vindex "&$port$&"
If this option is set to &"lmtp"& instead of &"smtp"&, the default value for
the &%port%& option changes to &"lmtp"&, and the transport operates the LMTP
protocol (RFC 2033) instead of SMTP. This protocol is sometimes used for local
deliveries into closed message stores. Exim also has support for running LMTP
over a pipe to a local process &-- see chapter &<<CHAPLMTP>>&.
+If this option is set to &"smtps"&, the default vaule for the &%port%& option
+changes to &"smtps"&, and the transport initiates TLS immediately after
+connecting, as an outbound SSL-on-connect, instead of using STARTTLS to upgrade.
+The Internet standards bodies strongly discourage use of this mode.
+
.option retry_include_ip_address smtp boolean true
Exim normally includes both the host name and the IP address in the key it
be the name of a file that contains a CRL in PEM format.
+.new
+.option tls_dh_min_bits smtp integer 1024
+.cindex "TLS" "Diffie-Hellman minimum acceptable size"
+When establishing a TLS session, if a ciphersuite which uses Diffie-Hellman
+key agreement is negotiated, the server will provide a large prime number
+for use. This option establishes the minimum acceptable size of that number.
+If the parameter offered by the server is too small, then the TLS handshake
+will fail.
+
+Only supported when using GnuTLS.
+.wen
+
+
.option tls_privatekey smtp string&!! unset
.cindex "TLS" "client private key, location of"
.vindex "&$host$&"
+.option tls_sni smtp string&!! unset
+.cindex "TLS" "Server Name Indication"
+.vindex "&$tls_sni$&"
+If this option is set then it sets the $tls_sni variable and causes any
+TLS session to pass this value as the Server Name Indication extension to
+the remote side, which can be used by the remote side to select an appropriate
+certificate and private key for the session.
+
+See &<<SECTtlssni>>& for more information.
+
+Note that for OpenSSL, this feature requires a build of OpenSSL that supports
+TLS extensions.
+
+
+
+
.option tls_tempfail_tryclear smtp boolean true
.cindex "4&'xx'& responses" "to STARTTLS"
When the server host is not in &%hosts_require_tls%&, and there is a problem in
.code
AUTH_CRAM_MD5=yes
AUTH_CYRUS_SASL=yes
+AUTH_DOVECOT=yes
+AUTH_GSASL=yes
+AUTH_HEIMDAL_GSSAPI=yes
AUTH_PLAINTEXT=yes
AUTH_SPA=yes
.endd
in &_Local/Makefile_&, respectively. The first of these supports the CRAM-MD5
authentication mechanism (RFC 2195), and the second provides an interface to
-the Cyrus SASL authentication library. The third can be configured to support
+the Cyrus SASL authentication library.
+The third is an interface to Dovecot's authentication system, delegating the
+work via a socket interface.
+The fourth provides an interface to the GNU SASL authentication library, which
+provides mechanisms but typically not data sources.
+The fifth provides direct access to Heimdal GSSAPI, geared for Kerberos, but
+supporting setting a server keytab.
+The sixth can be configured to support
the PLAIN authentication mechanism (RFC 2595) or the LOGIN mechanism, which is
-not formally documented, but used by several MUAs. The fourth authenticator
+not formally documented, but used by several MUAs. The seventh authenticator
supports Microsoft's &'Secure Password Authentication'& mechanism.
The authenticators are configured using the same syntax as other drivers (see
authenticators, followed by general discussion of the way authentication works
in Exim.
+&*Beware:*& the meaning of &$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.
+
.section "Generic options for authenticators" "SECID168"
is used directly to control authentication. See section &<<SECTplainserver>>&
for details.
+For the &(gsasl)& authenticator, this option is required for various
+mechanisms; see chapter &<<CHAPgsasl>>& for details.
+
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
server_prompts = Username:: : Password::
server_condition = ${if and{{ \
!eq{}{$auth1} }{ \
- ldapauth{user="cn=${quote_ldap_dn:$auth1},ou=people,o=example.org" \
- pass=${quote:$auth2} \
- ldap://ldap.example.org/} }} }
+ ldapauth{\
+ user="uid=${quote_ldap_dn:$auth1},ou=people,o=example.org" \
+ pass=${quote:$auth2} \
+ ldap://ldap.example.org/} }} }
server_set_id = uid=$auth1,ou=people,o=example.org
.endd
We have to check that the username is not empty before using it, because LDAP
Note that this expansion explicitly forces failure if the lookup fails
because &$auth1$& contains an unknown user name.
+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
.section "Using cram_md5 as a client" "SECID177"
.cindex "options" "&(cram_md5)& authenticator (client)"
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.
+
+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 &<<CHAPheimdalgss>>&
.section "Using cyrus_sasl as a server" "SECID178"
server_set_id = $auth1
.endd
-.option server_realm cyrus_sasl string unset
+.option server_realm cyrus_sasl string&!! unset
This specifies the SASL realm that the server claims to be in.
.ecindex IIDdcotauth2
+. ////////////////////////////////////////////////////////////////////////////
+. ////////////////////////////////////////////////////////////////////////////
+.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 4.80 release
+and there are a few areas where the library does not let Exim smoothly
+scale to handle future authentication mechanisms, so no guarantee can be
+made that any particular new authentication mechanism will be supported
+without code changes in Exim.
+
+
+.option server_channelbinding gsasl boolean 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
+
+
+. ////////////////////////////////////////////////////////////////////////////
+. ////////////////////////////////////////////////////////////////////////////
+
+.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$&: the &'authorization id'&, sent within SASL encapsulation after
+authentication. If that was empty, this will also be set to the
+GSS Display Name.
+.endlist
+
+
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
The &%tls_verify_certificates%& option must contain the name of a file, not the
name of a directory (for OpenSSL it can be either).
.next
-The &%tls_dhparam%& option is ignored, because early versions of GnuTLS had no
-facility for varying its Diffie-Hellman parameters. I understand that this has
-changed, but Exim has not been updated to provide this facility.
+The default value for &%tls_dhparam%& differs for historical reasons.
.next
.vindex "&$tls_peerdn$&"
Distinguished Name (DN) strings reported by the OpenSSL library use a slash for
affects the value of the &$tls_peerdn$& variable.
.next
OpenSSL identifies cipher suites using hyphens as separators, for example:
-DES-CBC3-SHA. GnuTLS uses underscores, for example: RSA_ARCFOUR_SHA. What is
-more, OpenSSL complains if underscores are present in a cipher list. To make
-life simpler, Exim changes underscores to hyphens for OpenSSL and hyphens to
-underscores for GnuTLS when processing lists of cipher suites in the
+DES-CBC3-SHA. GnuTLS historically used underscores, for example:
+RSA_ARCFOUR_SHA. What is more, OpenSSL complains if underscores are present
+in a cipher list. To make life simpler, Exim changes underscores to hyphens
+for OpenSSL and passes the string unchanged to GnuTLS (expecting the library
+to handle its own older variants) when processing lists of cipher suites in the
&%tls_require_ciphers%& options (the global option and the &(smtp)& transport
option).
.next
The &%tls_require_ciphers%& options operate differently, as described in the
sections &<<SECTreqciphssl>>& and &<<SECTreqciphgnu>>&.
+.next
+.new
+The &%tls_dh_min_bits%& SMTP transport option is only honoured by GnuTLS.
+When using OpenSSL, this option is ignored.
+(If an API is found to let OpenSSL be configured in this way,
+let the Exim Maintainers know and we'll likely use it).
+.wen
+.next
+Some other recently added features may only be available in one or the other.
+This should be documented with the feature. If the documentation does not
+explicitly state that the feature is infeasible in the other TLS
+implementation, then patches are welcome.
.endlist
-.section "GnuTLS parameter computation" "SECID181"
+.section "GnuTLS parameter computation" "SECTgnutlsparam"
+This section only applies if &%tls_dhparam%& is set to &`historic`& or to
+an explicit path; if the latter, then the text about generation still applies,
+but not the chosen filename.
+By default, as of Exim 4.80 a hard-coded D-H prime is used.
+See the documentation of &%tls_dhparam%& for more information.
+
GnuTLS uses D-H parameters that may take a substantial amount of time
to compute. It is unreasonable to re-compute them for every TLS session.
Therefore, Exim keeps this data in a file in its spool directory, called
-&_gnutls-params_&. The file is owned by the Exim user and is readable only by
+&_gnutls-params-NNNN_& for some value of NNNN, corresponding to the number
+of bits requested.
+The file is owned by the Exim user and is readable only by
its owner. Every Exim process that start up GnuTLS reads the D-H
parameters from this file. If the file does not exist, the first Exim process
that needs it computes the data and writes it to a temporary file which is
For maximum security, the parameters that are stored in this file should be
recalculated periodically, the frequency depending on your paranoia level.
+If you are avoiding using the fixed D-H primes published in RFCs, then you
+are concerned about some advanced attacks and will wish to do this; if you do
+not regenerate then you might as well stick to the standard primes.
+
Arranging this is easy in principle; just delete the file when you want new
values to be computed. However, there may be a problem. The calculation of new
parameters needs random numbers, and these are obtained from &_/dev/random_&.
a substantial amount of time, causing timeouts on incoming connections.
The solution is to generate the parameters externally to Exim. They are stored
-in &_gnutls-params_& in PEM format, which means that they can be generated
-externally using the &(certtool)& command that is part of GnuTLS.
+in &_gnutls-params-N_& in PEM format, which means that they can be
+generated externally using the &(certtool)& command that is part of GnuTLS.
To replace the parameters with new ones, instead of deleting the file
and letting Exim re-create it, you can generate new parameters using
&(certtool)& and, when this has been done, replace Exim's cache file by
renaming. The relevant commands are something like this:
.code
+# ls
+[ look for file; assume gnutls-params-2236 is the most recent ]
# rm -f new-params
# touch new-params
# chown exim:exim new-params
+# chmod 0600 new-params
+# certtool --generate-dh-params --bits 2236 >>new-params
+# openssl dhparam -noout -text -in new-params | head
+[ check the first line, make sure it's not more than 2236;
+ if it is, then go back to the start ("rm") and repeat
+ until the size generated is at most the size requested ]
# chmod 0400 new-params
-# certtool --generate-privkey --bits 512 >new-params
-# echo "" >>new-params
-# certtool --generate-dh-params --bits 1024 >> new-params
-# mv new-params gnutls-params
+# mv new-params gnutls-params-2236
.endd
If Exim never has to generate the parameters itself, the possibility of
stalling is removed.
+The filename changed in Exim 4.80, to gain the -bits suffix. The value which
+Exim will choose depends upon the version of GnuTLS in use. For older GnuTLS,
+the value remains hard-coded in Exim as 1024. As of GnuTLS 2.12.x, there is
+a way for Exim to ask for the "normal" number of bits for D-H public-key usage,
+and Exim does so. This attempt to remove Exim from TLS policy decisions
+failed, as GnuTLS 2.12 returns a value higher than the current hard-coded limit
+of the NSS library. Thus Exim gains the &%tls_dh_max_bits%& global option,
+which applies to all D-H usage, client or server. If the value returned by
+GnuTLS is greater than &%tls_dh_max_bits%& then the value will be clamped down
+to &%tls_dh_max_bits%&. The default value has been set at the current NSS
+limit, which is still much higher than Exim historically used.
+
+The filename and bits used will change as the GnuTLS maintainers change the
+value for their parameter &`GNUTLS_SEC_PARAM_NORMAL`&, as clamped by
+&%tls_dh_max_bits%&. At the time of writing (mid 2012), GnuTLS 2.12 recommends
+2432 bits, while NSS is limited to 2236 bits.
+
+In fact, the requested value will be *lower* than &%tls_dh_max_bits%&, to
+increase the chance of the generated prime actually being within acceptable
+bounds, as GnuTLS has been observed to overshoot. Note the check step in the
+procedure above. There is no sane procedure available to Exim to double-check
+the size of the generated prime, so it might still be too large.
+
.section "Requiring specific ciphers in OpenSSL" "SECTreqciphssl"
.cindex "TLS" "requiring specific ciphers (OpenSSL)"
suites before the cipher negotiation takes place. This specifies which ciphers
are acceptable. The list is colon separated and may contain names like
DES-CBC3-SHA. Exim passes the expanded value of &%tls_require_ciphers%&
-directly to this function call. The following quotation from the OpenSSL
+directly to this function call.
+Many systems will install the OpenSSL manual-pages, so you may have
+&'ciphers(1)'& available to you.
+The following quotation from the OpenSSL
documentation specifies what forms of item are allowed in the cipher string:
.ilist
not be moved to the end of the list.
.endlist
+The OpenSSL &'ciphers(1)'& command may be used to test the results of a given
+string:
+.code
+# note single-quotes to get ! past any shell history expansion
+$ openssl ciphers 'HIGH:!MD5:!SHA1'
+.endd
+
+This example will let the library defaults be permitted on the MX port, where
+there's probably no identity verification anyway, but ups the ante on the
+submission ports where the administrator might have some influence on the
+choice of clients used:
+.code
+# OpenSSL variant; see man ciphers(1)
+tls_require_ciphers = ${if =={$received_port}{25}\
+ {DEFAULT}\
+ {HIGH:!MD5:!SHA1}}
+.endd
+
.section "Requiring specific ciphers or other parameters in GnuTLS" &&&
.cindex "TLS" "specifying key exchange methods (GnuTLS)"
.cindex "TLS" "specifying MAC algorithms (GnuTLS)"
.cindex "TLS" "specifying protocols (GnuTLS)"
+.cindex "TLS" "specifying priority string (GnuTLS)"
.oindex "&%tls_require_ciphers%&" "GnuTLS"
-The GnuTLS library allows the caller to specify separate lists of permitted key
-exchange methods, main cipher algorithms, MAC algorithms, and protocols.
-Unfortunately, these lists are numerical, and the library does not have a
-function for turning names into numbers. Consequently, lists of recognized
-names have to be built into the application. The permitted key exchange
-methods, ciphers, and MAC algorithms may be used in any combination to form a
-cipher suite. This is unlike OpenSSL, where complete cipher suite names are
-passed to its control function.
-
-For compatibility with OpenSSL, the &%tls_require_ciphers%& option can be set
-to complete cipher suite names such as RSA_ARCFOUR_SHA, but for GnuTLS this
-option controls only the cipher algorithms. Exim searches each item in the
-list for the name of an available algorithm. For example, if the list
-contains RSA_AES_SHA, then AES is recognized, and the behaviour is exactly
-the same as if just AES were given.
-
-.oindex "&%gnutls_require_kx%&"
-.oindex "&%gnutls_require_mac%&"
-.oindex "&%gnutls_require_protocols%&"
-There are additional options called &%gnutls_require_kx%&,
-&%gnutls_require_mac%&, and &%gnutls_require_protocols%& that can be used to
-restrict the key exchange methods, MAC algorithms, and protocols, respectively.
-These options are ignored if OpenSSL is in use.
-
-All four options are available as global options, controlling how Exim
-behaves as a server, and also as options of the &(smtp)& transport, controlling
-how Exim behaves as a client. All the values are string expanded. After
-expansion, the values must be colon-separated lists, though the separator
-can be changed in the usual way.
-
-Each of the four lists starts out with a default set of algorithms. If the
-first item in a list does &'not'& start with an exclamation mark, all the
-default items are deleted. In this case, only those that are explicitly
-specified can be used. If the first item in a list &'does'& start with an
-exclamation mark, the defaults are left on the list.
-
-Then, any item that starts with an exclamation mark causes the relevant
-entry to be removed from the list, and any item that does not start with an
-exclamation mark causes a new entry to be added to the list. Unrecognized
-items in the list are ignored. Thus:
-.code
-tls_require_ciphers = !ARCFOUR
-.endd
-allows all the defaults except ARCFOUR, whereas
-.code
-tls_require_ciphers = AES : 3DES
-.endd
-allows only cipher suites that use AES or 3DES.
-
-For &%tls_require_ciphers%& the recognized names are AES_256, AES_128, AES
-(both of the preceding), 3DES, ARCFOUR_128, ARCFOUR_40, and ARCFOUR (both of
-the preceding). The default list does not contain all of these; it just has
-AES_256, AES_128, 3DES, and ARCFOUR_128.
-
-For &%gnutls_require_kx%&, the recognized names are DHE_RSA, RSA (which
-includes DHE_RSA), DHE_DSS, and DHE (which includes both DHE_RSA and
-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.
-
-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
-client, the order in the &%tls_require_ciphers%& list specifies a preference
-order for the cipher algorithms. The first one in the client's list that is
-also advertised by the server is tried first. The default order is as listed
-above.
+The GnuTLS library allows the caller to provide a "priority string", documented
+as part of the &[gnutls_priority_init]& function. This is very similar to the
+ciphersuite specification in OpenSSL.
+
+The &%tls_require_ciphers%& option is treated as the GnuTLS priority string.
+The &%tls_require_ciphers%& option is available both as an global option,
+controlling how Exim behaves as a server, and also as an option of the
+&(smtp)& transport, controlling how Exim behaves as a client. In both cases
+the value is string expanded. The resulting string is not an Exim list and
+the string is given to the GnuTLS library, so that Exim does not need to be
+aware of future feature enhancements of GnuTLS.
+
+Documentation of the strings accepted may be found in the GnuTLS manual, under
+"Priority strings". This is online as
+&url(http://www.gnu.org/software/gnutls/manual/html_node/Priority-Strings.html),
+but beware that this relates to GnuTLS 3, which may be newer than the version
+installed on your system. If you are using GnuTLS 3,
+&url(http://www.gnu.org/software/gnutls/manual/html_node/Listing-the-ciphersuites-in-a-priority-string.html, then the example code)
+on that site can be used to test a given string.
+
+Prior to Exim 4.80, an older API of GnuTLS was used, and Exim supported three
+additional options, "&%gnutls_require_kx%&", "&%gnutls_require_mac%&" and
+"&%gnutls_require_protocols%&". &%tls_require_ciphers%& was an Exim list.
+
+This example will let the library defaults be permitted on the MX port, where
+there's probably no identity verification anyway, and lowers security further
+by increasing compatibility; but this ups the ante on the submission ports
+where the administrator might have some influence on the choice of clients
+used:
+.code
+# GnuTLS variant
+tls_require_ciphers = ${if =={$received_port}{25}\
+ {NORMAL:%COMPAT}\
+ {SECURE128}}
+.endd
.section "Configuring an Exim server to use TLS" "SECID182"
tls_dhparam = /some/file/name
.endd
is set, the SSL library is initialized for the use of Diffie-Hellman ciphers
-with the parameters contained in the file. This increases the set of cipher
-suites that the server supports. See the command
+with the parameters contained in the file.
+Set this to &`none`& to disable use of DH entirely, by making no prime
+available:
+.code
+tls_dhparam = none
+.endd
+This may also be set to a string identifying a standard prime to be used for
+DH; if it is set to &`default`& or, for OpenSSL, is unset, then the prime
+used is &`ike23`&. There are a few standard primes available, see the
+documetnation for &%tls_dhparam%& for the complete list.
+
+See the command
.code
openssl dhparam
.endd
-for a way of generating this data. At present, &%tls_dhparam%& is used only
-when Exim is linked with OpenSSL. It is ignored if GnuTLS is being used.
+for a way of generating file data.
The strings supplied for these three options are expanded every time a client
host connects. It is therefore possible to use different certificates and keys
which the client is connected. Forced failure of an expansion causes Exim to
behave as if the relevant option were unset.
+.vindex &$tls_bits$&
.vindex &$tls_cipher$&
.vindex &$tls_peerdn$&
-Before an SMTP connection is established, the &$tls_cipher$& and &$tls_peerdn$&
+.vindex &$tls_sni$&
+Before an SMTP connection is established, the
+&$tls_bits$&, &$tls_cipher$&, &$tls_peerdn$& and &$tls_sni$&
variables are emptied. (Until the first connection, they contain the values
that were set when the message was received.) If STARTTLS is subsequently
successfully obeyed, these variables are set to the relevant values for the
+.section "Use of TLS Server Name Indication" "SECTtlssni"
+.cindex "TLS" "Server Name Indication"
+.vindex "&$tls_sni$&"
+.oindex "&%tls_sni%&"
+With TLS1.0 or above, there is an extension mechanism by which extra
+information can be included at various points in the protocol. One of these
+extensions, documented in RFC 6066 (and before that RFC 4366) is
+&"Server Name Indication"&, commonly &"SNI"&. This extension is sent by the
+client in the initial handshake, so that the server can examine the servername
+within and possibly choose to use different certificates and keys (and more)
+for this session.
+
+This is analagous to HTTP's &"Host:"& header, and is the main mechanism by
+which HTTPS-enabled web-sites can be virtual-hosted, many sites to one IP
+address.
+
+With SMTP to MX, there are the same problems here as in choosing the identity
+against which to validate a certificate: you can't rely on insecure DNS to
+provide the identity which you then cryptographically verify. So this will
+be of limited use in that environment.
+
+With SMTP to Submission, there is a well-defined hostname which clients are
+connecting to and can validate certificates against. Thus clients &*can*&
+choose to include this information in the TLS negotiation. If this becomes
+wide-spread, then hosters can choose to present different certificates to
+different clients. Or even negotiate different cipher suites.
+
+The &%tls_sni%& option on an SMTP transport is an expanded string; the result,
+if not empty, will be sent on a TLS session as part of the handshake. There's
+nothing more to it. Choosing a sensible value not derived insecurely is the
+only point of caution. The &$tls_sni$& variable will be set to this string
+for the lifetime of the client connection (including during authentication).
+
+Except during SMTP client sessions, if &$tls_sni$& is set then it is a string
+received from a client.
+It can be logged with the &%log_selector%& item &`+tls_sni`&.
+
+If the string &`tls_sni`& appears in the main section's &%tls_certificate%&
+option (prior to expansion) then the following options will be re-expanded
+during TLS session handshake, to permit alternative values to be chosen:
+
+.ilist
+.vindex "&%tls_certificate%&"
+&%tls_certificate%&
+.next
+.vindex "&%tls_crl%&"
+&%tls_crl%&
+.next
+.vindex "&%tls_privatekey%&"
+&%tls_privatekey%&
+.next
+.vindex "&%tls_verify_certificates%&"
+&%tls_verify_certificates%&
+.endlist
+
+Great care should be taken to deal with matters of case, various injection
+attacks in the string (&`../`& or SQL), and ensuring that a valid filename
+can always be referenced; it is important to remember that &$tls_sni$& is
+arbitrary unverified data provided prior to authentication.
+
+The Exim developers are proceeding cautiously and so far no other TLS options
+are re-expanded.
+
+When Exim is built againt OpenSSL, OpenSSL must have been built with support
+for TLS Extensions. This holds true for OpenSSL 1.0.0+ and 0.9.8+ with
+enable-tlsext in EXTRACONFIGURE. If you invoke &(openssl s_client -h)& and
+see &`-servername`& in the output, then OpenSSL has support.
+
+When Exim is built against GnuTLS, SNI support is available as of GnuTLS
+0.5.10. (Its presence predates the current API which Exim uses, so if Exim
+built, then you have SNI support).
+
+
+
.section "Multiple messages on the same encrypted TCP/IP connection" &&&
"SECTmulmessam"
.cindex "multiple SMTP deliveries with TLS"
your resources.
+.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).
+
+The ACL test specified by &%acl_smtp_dkim%& happens after a message has been
+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 &<<CHID12>>&.
+
+
.section "The SMTP MIME ACL" "SECID194"
The &%acl_smtp_mime%& option is available only when Exim is compiled with the
content-scanning extension. For details, see chapter &<<CHAPexiscan>>&.
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"
control = debug/opts=+expand+acl
control = debug/tag=.$message_exim_id/opts=+expand
.endd
-.wen
+
.vitem &*control&~=&~enforce_sync*& &&&
&*control&~=&~no_enforce_sync*&
&`$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 &<<rearatdat>>&).
-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 &<<ratoptuniq>>& 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.
-.section "Ratelimit options for handling fast clients" "ratophanfas"
+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
+
+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
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
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 $sender_rate_limit)
-.endd
-In this example, the rate is tested and used to deny access (when it is too
-high) in the connect ACL, but the actual computation of the remembered rate
-happens later, on a per-command basis, in another ACL.
-
-
.section "Address verification" "SECTaddressverification"
.cindex "verifying address" "options for"
really random &-- it is defined by the expansion of the option
&%callout_random_local_part%&, which defaults to
.code
-$primary_host_name-$tod_epoch-testing
+$primary_hostname-$tod_epoch-testing
.endd
The idea here is to try to determine whether the remote host accepts all local
parts without checking. If it does, there is no point in doing callouts for
specialized interfaces for &"daemon"& type virus scanners, which are resident
in memory and thus are much faster.
+
.oindex "&%av_scanner%&"
You can set the &%av_scanner%& option in first part of the Exim configuration
file to specify which scanner to use, together with any additional options that
av_scanner = aveserver:/var/run/aveserver
.endd
+
.vitem &%clamd%&
.cindex "virus scanners" "clamd"
This daemon-type scanner is GPL and free. You can get it at
use the &%demime%& condition (see section &<<SECTdemimecond>>&) before the
&%malware%& condition.
-.new
Beware the interaction of Exim's &%message_size_limit%& with any size limits
imposed by your anti-virus scanner.
-.wen
Here is a very simple scanning example:
.code
&%spam%& condition for its side effects (see the variables below), you can make
it always return &"true"& by appending &`:true`& to the username.
-.new
.cindex "spam scanning" "returned variables"
When the &%spam%& condition is run, it sets up a number of expansion
variables. These variables are saved with the received message, thus they are
available for use at delivery time.
-.wen
.vlist
.vitem &$spam_score$&
because &$spam_score$& is rounded and &$spam_score_int$& is truncated.
The integer value is useful for numeric comparisons in conditions.
-
.vitem &$spam_bar$&
A string consisting of a number of &"+"& or &"-"& characters, representing the
integer part of the spam score value. A spam score of 4.4 would have a
If you do not specify anything at build time or run time, that is where the
logs are written.
-A log file path may also contain &`%D`& if datestamped log file names are in
-use &-- see section &<<SECTdatlogfil>>& below.
+A log file path may also contain &`%D`& or &`%M`& if datestamped log file names
+are in use &-- see section &<<SECTdatlogfil>>& below.
Here are some examples of possible settings:
.display
.cindex "log" "datestamped files"
Instead of cycling the main and reject log files by renaming them
periodically, some sites like to use files whose names contain a datestamp,
-for example, &_mainlog-20031225_&. The datestamp is in the form &_yyyymmdd_&.
-Exim has support for this way of working. It is enabled by setting the
-&%log_file_path%& option to a path that includes &`%D`& at the point where the
-datestamp is required. For example:
+for example, &_mainlog-20031225_&. The datestamp is in the form &_yyyymmdd_& or
+&_yyyymm_&. Exim has support for this way of working. It is enabled by setting
+the &%log_file_path%& option to a path that includes &`%D`& or &`%M`& at the
+point where the datestamp is required. For example:
.code
log_file_path = /var/spool/exim/log/%slog-%D
log_file_path = /var/log/exim-%s-%D.log
log_file_path = /var/spool/exim/log/%D-%slog
+log_file_path = /var/log/exim/%s.%M
.endd
As before, &`%s`& is replaced by &"main"& or &"reject"&; the following are
examples of names generated by the above examples:
/var/spool/exim/log/mainlog-20021225
/var/log/exim-reject-20021225.log
/var/spool/exim/log/20021225-mainlog
+/var/log/exim/main.200212
.endd
When this form of log file is specified, Exim automatically switches to new
files at midnight. It does not make any attempt to compress old logs; you
The location of the panic log is also determined by &%log_file_path%&, but it
is not datestamped, because rotation of the panic log does not make sense.
-When generating the name of the panic log, &`%D`& is removed from the string.
-In addition, if it immediately follows a slash, a following non-alphanumeric
-character is removed; otherwise a preceding non-alphanumeric character is
-removed. Thus, the three examples above would give these panic log names:
+When generating the name of the panic log, &`%D`& or &`%M`& are removed from
+the string. In addition, if it immediately follows a slash, a following
+non-alphanumeric character is removed; otherwise a preceding non-alphanumeric
+character is removed. Thus, the four examples above would give these panic
+log names:
.code
/var/spool/exim/log/paniclog
/var/log/exim-panic.log
/var/spool/exim/log/paniclog
+/var/log/exim/panic
.endd
&` tls_certificate_verified `& certificate verification status
&`*tls_cipher `& TLS cipher suite on <= and => lines
&` tls_peerdn `& TLS peer DN on <= and => lines
+&` tls_sni `& TLS SNI on <= lines
&` unknown_in_list `& DNS lookup failed in list match
&` all `& all of the above
connection, and a certificate is supplied by the remote host, the peer DN is
added to the log line, preceded by DN=.
.next
+.cindex "log" "TLS SNI"
+.cindex "TLS" "logging SNI"
+&%tls_sni%&: When a message is received over an encrypted connection, and
+the remote host provided the Server Name Indication extension, the SNI is
+added to the log line, preceded by SNI=.
+.next
.cindex "log" "DNS failure in list"
&%unknown_in_list%&: This setting causes a log entry to be written when the
result of a list match is failure because a DNS lookup failed.
In order to see the contents of messages on the queue, and to operate on them,
&'eximon'& must either be run as root or by an admin user.
+The command-line parameters of &'eximon'& are passed to &_eximon.bin_& and may
+contain X11 resource parameters interpreted by the X11 library. In addition,
+if the first parameter starts with the string "gdb" then it is removed and the
+binary is invoked under gdb (the parameter is used as the gdb command-name, so
+versioned variants of gdb can be invoked).
+
The monitor's window is divided into three parts. The first contains one or
more stripcharts and two action buttons, the second contains a &"tail"& of the
main log file, and the third is a display of the queue of messages awaiting
into the Exim account from running a privileged Exim with an arbitrary
configuration file, and using it to break into other accounts.
.next
-.new
+
If a non-trusted configuration file (i.e. not the default configuration file
or one which is trusted by virtue of being listed in the TRUSTED_CONFIG_LIST
file) is specified with &%-C%&, or if macros are given with &%-D%& (but see
it re-execs 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.
-.wen
+
.next
The WHITELIST_D_MACROS build option declares some macros to be safe to override
with &%-D%& if the real uid is one of root, the Exim run-time user or the
-
.section "Root privilege" "SECID270"
.cindex "setuid"
.cindex "root privilege"
+.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.
+
+
.section "Use of sprintf()" "SECID279"
.cindex "&[sprintf()]&"
A large number of occurrences of &"sprintf"& in the code are actually calls to
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
-.chapter "Support for DKIM (DomainKeys Identified Mail) - RFC4871" "CHID12" &&&
+.chapter "Support for DKIM (DomainKeys Identified Mail)" "CHID12" &&&
"DKIM Support"
.cindex "DKIM"
+DKIM is a mechanism by which messages sent by some entity can be provably
+linked to a domain which that entity controls. It permits reputation to
+be tracked on a per-domain basis, rather than merely upon source IP address.
+DKIM is documented in RFC 4871.
+
Since version 4.70, DKIM support is compiled into Exim by default. It can be
disabled by setting DISABLE_DKIM=yes in Local/Makefile.
Please note that verification of DKIM signatures in incoming mail is turned
on by default for logging purposes. For each signature in incoming email,
exim will log a line displaying the most important signature details, and the
-signature status. Here is an example:
+signature status. Here is an example (with line-breaks added for clarity):
.code
-2009-09-09 10:22:28 1MlIRf-0003LU-U3 DKIM: d=facebookmail.com s=q1-2009b c=relaxed/relaxed a=rsa-sha1 i=@facebookmail.com t=1252484542 [verification succeeded]
+2009-09-09 10:22:28 1MlIRf-0003LU-U3 DKIM:
+ d=facebookmail.com s=q1-2009b
+ c=relaxed/relaxed a=rsa-sha1
+ i=@facebookmail.com t=1252484542 [verification succeeded]
.endd
You might want to turn off DKIM verification processing entirely for internal
or relay mail sources. To do that, set the &%dkim_disable_verify%& ACL
Inside the &%acl_smtp_dkim%&, the following expansion variables are
available (from most to least important):
+
.vlist
.vitem &%$dkim_cur_signer%&
The signer that is being evaluated in this ACL run. This can be a domain or
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
verb to a group of domains or identities. For example:
.code
-# Warn when message apparently from GMail has no signature at all
+# Warn when Mail purportedly from GMail has no signature at all
warn log_message = GMail sender without DKIM signature
sender_domains = gmail.com
dkim_signers = gmail.com
.vitem &%dkim_status%&
ACL condition that checks a colon-separated list of possible DKIM verification
results agains the actual result of verification. This is typically used
-to restrict an ACL verb to a list of verification outcomes, like:
+to restrict an ACL verb to a list of verification outcomes, for example:
.code
-deny message = Message from Paypal with invalid or missing signature
+deny message = Mail from Paypal with invalid/missing signature
sender_domains = paypal.com:paypal.de
dkim_signers = paypal.com:paypal.de
dkim_status = none:invalid:fail
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