.section "Exim documentation" "SECID1"
. Keep this example change bar when updating the documentation!
+.new
.cindex "documentation"
This edition of the Exim specification applies to version &version() of Exim.
Substantive changes from the &previousversion; edition are marked in some
renditions of this document; this paragraph is so marked if the rendition is
capable of showing a change indicator.
+.wen
This document is very much a reference manual; it is not a tutorial. The reader
is expected to have some familiarity with the SMTP mail transfer protocol and
in &_Local/Makefile_&.
.wen
+.new
If OpenSSL is installed, you should set
.code
USE_OPENSL=yes
in &_Local/Makefile_&. You may also need to specify the locations of the
OpenSSL library and include files. For example:
.code
-USE_OPENSL=yes
+USE_OPENSSL=yes
TLS_LIBS=-L/usr/local/openssl/lib -lssl -lcrypto
TLS_INCLUDE=-I/usr/local/openssl/include/
.endd
.cindex "pkg-config" "OpenSSL"
If you have &'pkg-config'& available, then instead you can just use:
.code
-USE_OPENSL=yes
+USE_OPENSSL=yes
USE_OPENSSL_PC=openssl
.endd
+.wen
.cindex "USE_GNUTLS"
If GnuTLS is installed, you should set
.code
user.
.new
-.vitem &%-MG%&&~<&'queue&~name'&&~<&'message&~id'&>&~<&'message&~id'&>&~...
+.vitem &%-MG%&&~<&'queue&~name'&>&~<&'message&~id'&>&~<&'message&~id'&>&~...
.oindex "&%-MG%&"
.cindex queue named
.cindex "named queues"
This transport is used for delivering messages over SMTP connections.
The list of remote hosts comes from the router.
The &%message_size_limit%& usage is a hack to avoid sending on messages
-with over-long lines. The built-in macro _HAVE_DANE guards configuration
-to use DANE for delivery;
-see section &<<SECDANE>>& for more details.
+with over-long lines.
The &%hosts_try_prdr%& option enables an efficiency SMTP option. It is
negotiated between client and server and not expected to cause problems
With &"strict"& a response from the DNS resolver that
is not labelled as authenticated data
is treated as equivalent to a temporary DNS error.
+.new
The default is &"lax"&.
+.wen
See also the &$lookup_dnssec_authenticated$& variable.
&<<CHAPTLS>>& for details of TLS support and chapter &<<CHAPsmtptrans>>& for
details of the &(smtp)& transport.
-,new
+.new
.vitem &$tls_out_cipher_std$&
.vindex "&$tls_out_cipher_std$&"
As above, but returning the RFC standard name for the cipher suite.
.vindex &$tls_out_tlsa_usage$&
Bitfield of TLSA record types found. See section &<<SECDANE>>&.
+.new
+.vitem &$tls_in_ver$&
+.vindex "&$tls_in_ver$&"
+When a message is received from a remote host over an encrypted SMTP connection
+this variable is set to the protocol version, eg &'TLS1.2'&.
+
+.vitem &$tls_out_ver$&
+.vindex "&$tls_out_ver$&"
+When a message is being delivered to a remote host over an encrypted SMTP connection
+this variable is set to the protocol version.
+.wen
+
+
.vitem &$tod_bsdinbox$&
.vindex "&$tod_bsdinbox$&"
The time of day and the date, in the format required for BSD-style mailbox
.option add_environment main "string list" empty
.cindex "environment" "set values"
-This option allows to set individual environment variables that the
-currently linked libraries and programs in child processes use.
+This option adds individual environment variables that the
+currently linked libraries and programs in child processes may use.
+Each list element should be of the form &"name=value"&.
+
See &<<SECTpipeenv>>& for the environment of &(pipe)& transports.
.option admin_groups main "string list&!!" unset
used. See chapter &<<CHAPsecurity>>& for a discussion of security issues.
+.new
.option exim_version main string "current version"
.cindex "Exim version"
.cindex customizing "version number"
.cindex "version number of Exim" override
-This option allows to override the &$version_number$&/&$exim_version$& Exim reports in
-various places. Use with care, this may fool stupid security scanners.
+This option overrides the &$version_number$&/&$exim_version$& that Exim reports in
+various places. Use with care; this may fool stupid security scanners.
+.wen
.option extra_local_interfaces main "string list" unset
This option is available only when Exim is built with an embedded Perl
interpreter. See chapter &<<CHAPperl>>& for details of its use.
-.option perl_startup main boolean false
+.option perl_taintmode main boolean false
.cindex "Perl"
-This Option enables the taint mode of the embedded Perl interpreter.
+This option enables the taint mode of the embedded Perl interpreter.
.option pgsql_servers main "string list" unset
${if def:sender_helo_name {(helo=$sender_helo_name)\n\t}}}}\
by $primary_hostname \
${if def:received_protocol {with $received_protocol }}\
+ ${if def:tls_ver { ($tls_ver)}}\
${if def:tls_in_cipher_std { tls $tls_in_cipher_std\n\t}}\
(Exim $version_number)\n\t\
${if def:sender_address \
&%sender_unqualified_hosts%&, or if the message was submitted locally (not
using TCP/IP), and the &%-bnq%& option was not set.
-.option add_environment main "string list" empty
-.cindex "environment"
-This option allows to add individual environment variables that the
-currently linked libraries and programs in child processes use. The
-default list is empty.
-
.option slow_lookup_log main integer 0
.cindex "logging" "slow lookups"
The list separator is a semicolon but can be changed in the
usual way.
-Each list-element given must be of the form $"name = value"$
+Each list-element given must be of the form &"name = value"&
and the names used must start with the string &"r_"&.
Values containing a list-separator should have them doubled.
When a router runs, the strings are evaluated in order,
(not including any preconditions)
and by the transport.
Later definitions of a given named variable will override former ones.
-Varible use is via the usual &$r_...$& syntax.
+Variable use is via the usual &$r_...$& syntax.
This is similar to the &%address_data%& option, except that
many independent variables can be used, with choice of naming.
use unencrypted plain text, you should not use the same passwords for SMTP
connections as you do for login accounts.
-.section "Plaintext options" "SECID171"
+.new
+.section "Avoiding cleartext use" "SECTplain_TLS"
+The following generic option settings will disable &(plaintext)& authenticators when
+TLS is not being used:
+.code
+ server_advertise_condition = ${if def:tls_in_cipher }
+ client_condition = ${if def:tls_out_cipher}
+.endd
+
+&*Note*&: a plaintext SMTP AUTH done inside TLS is not vulnerable to casual snooping,
+but is still vulnerable to a Man In The Middle attack unless certificates
+(including their names) have been properly verified.
+.wen
+
+.section "Plaintext server options" "SECID171"
.cindex "options" "&(plaintext)& authenticator (server)"
When configured as a server, &(plaintext)& uses the following options:
This is actually a global authentication option, but it must be set in order to
configure the &(plaintext)& driver as a server. Its use is described below.
-.option server_prompts plaintext string&!! unset
+.option server_prompts plaintext "string list&!!" unset
The contents of this option, after expansion, must be a colon-separated list of
prompt strings. If expansion fails, a temporary authentication rejection is
given.
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
+.new
.chapter "The external authenticator" "CHAPexternauth"
.scindex IIDexternauth1 "&(external)& authenticator"
.scindex IIDexternauth2 "authenticators" "&(external)&"
(which usually means the full set of public CAs)
and which has a mail-SAN matching the claimed identity sent by the client.
-Note that, up to TLS1.2, the client cert is on the wire in-clear, including the SAN,
+&*Note*&: up to TLS1.2, the client cert is on the wire in-clear, including the SAN.
The account name is therefore guessable by an opponent.
TLS 1.3 protects both server and client certificates, and is not vulnerable
in this way.
-Likewise, a traditional plaintext SMTP AUTH done inside TLS is not.
.section "Using external in a client" "SECTexternclient"
.ecindex IIDexternauth1
.ecindex IIDexternauth2
+.wen
.section "OpenSSL vs GnuTLS" "SECTopenvsgnu"
.cindex "TLS" "OpenSSL &'vs'& GnuTLS"
-The first TLS support in Exim was implemented using OpenSSL. Support for GnuTLS
-followed later, when the first versions of GnuTLS were released. To build Exim
-to use GnuTLS, you need to set
+TLS is supported in Exim using either the OpenSSL or GnuTLS library.
+.new
+To build Exim to use OpenSSL you need to set
+.code
+USE_OPENSSL=yes
+.endd
+in Local/Makefile.
+.wen
+
+To build Exim to use GnuTLS, you need to set
.code
USE_GNUTLS=yes
.endd
-in Local/Makefile
-you must also set TLS_LIBS and TLS_INCLUDE appropriately, so that the
+in Local/Makefile.
+
+You must also set TLS_LIBS and TLS_INCLUDE appropriately, so that the
include files and libraries for GnuTLS can be found.
There are some differences in usage when using GnuTLS instead of OpenSSL:
&%tls_verify_hosts%& or &%tls_try_verify_hosts%& matches the client.
.new
-Do not use a certificate which has the OCSP-must-staple extension,
+&*Note*&: Do not use a certificate which has the OCSP-must-staple extension,
for client use (they are usable for server use).
-As TLS has no means for the client to staple before TLS 1.3 it will result
+As the TLS protocol has no means for the client to staple before TLS 1.3 it will result
in failed connections.
.wen
For client-side DANE there are three new smtp transport options, &%hosts_try_dane%&, &%hosts_require_dane%&
and &%dane_require_tls_ciphers%&.
-The require variant will result in failure if the target host is not
+The &"require"& variant will result in failure if the target host is not
DNSSEC-secured. To get DNSSEC-secured hostname resolution, use
the &%dnssec_request_domains%& router or transport option.
verification evaluation is wanted, the above variables should be set appropriately.
The router and transport option &%dnssec_request_domains%& must not be
-set to "never" and &%dnssec_require_domains%& is ignored.
+set to &"never"&, and &%dnssec_require_domains%& is ignored.
If verification was successful using DANE then the "CV" item in the delivery log line will show as "CV=dane".
the operation and configuration of DKIM, see section &<<SECDKIM>>&.
+.vitem &*control&~=&~dmarc_disable_verify*&
+.cindex "disable DMARC verify"
+.cindex "DMARC" "disable verify"
+This control turns off DMARC verification processing entirely. For details on
+the operation and configuration of DMARC, see section &<<SECDMARC>>&.
+
+
.vitem &*control&~=&~dscp/*&<&'value'&>
.cindex "&ACL;" "setting DSCP value"
.cindex "DSCP" "inbound"
This function is used in conjunction with &'smtp_printf()'&, as described
below.
-.vitem &*void&~smtp_printf(char&~*,&~...)*&
-The arguments of this function are like &[printf()]&; it writes to the SMTP
+.new
+.vitem &*void&~smtp_printf(char&~*,BOOL,&~...)*&
+The arguments of this function are almost like &[printf()]&; it writes to the SMTP
+.wen
output stream. You should use this function only when there is an SMTP output
stream, that is, when the incoming message is being received via interactive
SMTP. This is the case when &%smtp_input%& is TRUE and &%smtp_batched_input%&
If an SMTP TLS connection is established, &'smtp_printf()'& uses the TLS
output function, so it can be used for all forms of SMTP connection.
+.new
+The second argument is used to request that the data be buffered
+(when TRUE) or flushed (along with any previously buffered, when FALSE).
+This is advisory only, but likely to save on system-calls and packets
+sent when a sequence of calls to the function are made.
+
+The argument was added in Exim version 4.90 - changing the API/ABI.
+Nobody noticed until 4.93 was imminent, at which point the
+ABI version number was incremented.
+.wen
+
Strings that are written by &'smtp_printf()'& from within &[local_scan()]&
must start with an appropriate response code: 550 if you are going to return
LOCAL_SCAN_REJECT, 451 if you are going to return
multiple output lines.
The &'smtp_printf()'& function does not return any error indication, because it
-does not automatically flush pending output, and therefore does not test
+does not
+.new
+guarantee a flush of
+.wen
+pending output, and therefore does not test
the state of the stream. (In the main code of Exim, flushing and error
detection is done when Exim is ready for the next SMTP input command.) If
you want to flush the output and check for an error (for example, the
arguments. It flushes the output stream, and returns a non-zero value if there
is an error.
-.vitem &*void&~*store_get(int)*&
+.new
+.vitem &*void&~*store_get(int,BOOL)*&
This function accesses Exim's internal store (memory) manager. It gets a new
-chunk of memory whose size is given by the argument. Exim bombs out if it ever
+chunk of memory whose size is given by the first argument.
+The second argument should be given as TRUE if the memory will be used for
+data possibly coming from an attacker (eg. the message content),
+FALSE if it is locally-sourced.
+Exim bombs out if it ever
runs out of memory. See the next section for a discussion of memory handling.
+.wen
-.vitem &*void&~*store_get_perm(int)*&
+.vitem &*void&~*store_get_perm(int,BOOL)*&
This function is like &'store_get()'&, but it always gets memory from the
permanent pool. See the next section for a discussion of memory handling.
For building Exim yourself, obtain the library from
&url(http://sourceforge.net/projects/opendmarc/)
-to obtain a copy, or find it in your favorite rpm package
+to obtain a copy, or find it in your favorite package
repository. You will need to attend to the local/Makefile feature
SUPPORT_DMARC and the associated LDFLAGS addition.
This description assumes
status of messages coming from remote, untrusted sources. You can
use standard conditions such as hosts, senders, etc, to decide that
DMARC verification should *not* be performed for them and disable
-DMARC with a control setting:
+DMARC with an ACL control modifier:
.code
control = dmarc_disable_verify
.endd
be subscribed to, etc). You must configure exim to submit forensic
reports to the owner of the domain. If the DMARC record contains a
forensic address and you specify the control statement below, then
-exim will send these forensic emails. It's also advised that you
-configure a dmarc_forensic_sender because the default sender address
+exim will send these forensic emails. It is also advised that you
+configure a &%dmarc_forensic_sender%& because the default sender address
construction might be inadequate.
.code
control = dmarc_enable_forensic
.endd
(AGAIN: You can choose not to send these forensic reports by simply
not putting the dmarc_enable_forensic control line at any point in
-your exim config. If you don't tell it to send them, it will not
+your exim config. If you don't tell exim to send them, it will not
send them.)
There are no options to either control. Both must appear before
. subsection
DMARC checks cam be run on incoming SMTP messages by using the
-"dmarc_status" ACL condition in the DATA ACL. You are required to
-call the "spf" condition first in the ACLs, then the "dmarc_status"
+&"dmarc_status"& ACL condition in the DATA ACL. You are required to
+call the &"spf"& condition first in the ACLs, then the &"dmarc_status"&
condition. Putting this condition in the ACLs is required in order
for a DMARC check to actually occur. All of the variables are set
up before the DATA ACL, but there is no actual DMARC check that
-occurs until a "dmarc_status" condition is encountered in the ACLs.
+occurs until a &"dmarc_status"& condition is encountered in the ACLs.
-The dmarc_status condition takes a list of strings on its
+The &"dmarc_status"& condition takes a list of strings on its
right-hand side. These strings describe recommended action based
on the DMARC check. To understand what the policy recommendations
mean, refer to the DMARC website above. Valid strings are:
processed, and you can use them in this ACL. The following
expansion variables are available:
-&$dmarc_status$&
+.vlist
+.vitem &$dmarc_status$&
.vindex &$dmarc_status$&
.cindex DMARC result
-is a one word status indicating what the DMARC library
+A one word status indicating what the DMARC library
thinks of the email. It is a combination of the results of
DMARC record lookup and the SPF/DKIM/DMARC processing results
(if a DMARC record was found). The actual policy declared
in the DMARC record is in a separate expansion variable.
-&$dmarc_status_text$&
+.vitem &$dmarc_status_text$&
.vindex &$dmarc_status_text$&
-is a slightly longer, human readable status.
+Slightly longer, human readable status.
-&$dmarc_used_domain$&
+.vitem &$dmarc_used_domain$&
.vindex &$dmarc_used_domain$&
-is the domain which DMARC used to look up the DMARC policy record.
+The domain which DMARC used to look up the DMARC policy record.
-&$dmarc_domain_policy$&
+.vitem &$dmarc_domain_policy$&
.vindex &$dmarc_domain_policy$&
-is the policy declared in the DMARC record. Valid values
+The policy declared in the DMARC record. Valid values
are "none", "reject" and "quarantine". It is blank when there
is any error, including no DMARC record.
+.endlist
. subsection
In order to log statistics suitable to be imported by the opendmarc
tools, you need to:
.ilist
-Configure the global setting dmarc_history_file
+Configure the global option &%dmarc_history_file%&
.next
Configure cron jobs to call the appropriate opendmarc history
import scripts and truncating the dmarc_history_file
In order to send forensic reports, you need to:
.ilist
-Configure the global setting dmarc_forensic_sender
+Configure the global option &%dmarc_forensic_sender%&
.next
Configure, somewhere before the DATA ACL, the control option to
enable sending DMARC forensic reports
git://git.exim.org / exim.git / blobdiff