. Update the Copyright year (only) when changing content.
. /////////////////////////////////////////////////////////////////////////////
-.set previousversion "4.89"
+.set previousversion "4.90"
.include ./local_params
.set ACL "access control lists (ACLs)"
the same lookup again. Otherwise, because each Exim process caches the results
of lookups, you will just get the same result as before.
-.new
Macro processing is done on lines before string-expansion: new macros can be
defined and macros will be expanded.
Because macros in the config file are often used for secrets, those are only
available to admin users.
-.wen
.vitem &%-bem%&&~<&'filename'&>
.oindex "&%-bem%&"
by Exim in conjunction with the &%-MC%& option, and passes on the fact that the
host to which Exim is connected supports TLS encryption.
-.new
.vitem &%-MCt%&&~<&'IP&~address'&>&~<&'port'&>&~<&'cipher'&>
.oindex "&%-MCt%&"
This option is not intended for use by external callers. It is used internally
by Exim in conjunction with the &%-MC%& option, and passes on the fact that the
connection is being proxied by a parent process for handling TLS encryption.
The arguments give the local address and port being proxied, and the TLS cipher.
-.wen
.vitem &%-Mc%&&~<&'message&~id'&>&~<&'message&~id'&>&~...
.oindex "&%-Mc%&"
hexadecimal digits. There may be fewer than eight components if an empty
component (adjacent colons) is present. Only one empty component is permitted.
-.new
&*Note*&: The checks used to be just on the form of the address; actual numerical
values were not considered. Thus, for example, 999.999.999.999 passed the IPv4
check.
This is no longer the case.
-.wen
The main use of these tests is to distinguish between IP addresses and
host names, or between IPv4 and IPv6 addresses. For example, you could use
.vindex "&$config_file$&"
The name of the main configuration file Exim is using.
+.vitem &$dkim_verify_status$& &&&
+Results of DKIM verification.
+For details see section &<<SECDKIMVFY>>&.
+
.vitem &$dkim_cur_signer$& &&&
- &$dkim_verify_status$& &&&
&$dkim_verify_reason$& &&&
&$dkim_domain$& &&&
&$dkim_identity$& &&&
&$dkim_key_notes$& &&&
&$dkim_key_length$&
These variables are only available within the DKIM ACL.
-For details see chapter &<<CHAPdkim>>&.
+For details see section &<<SECDKIMVFY>>&.
.vitem &$dkim_signers$&
.vindex &$dkim_signers$&
When a message has been received this variable contains
a colon-separated list of signer domains and identities for the message.
-For details see chapter &<<CHAPdkim>>&.
+For details see section &<<SECDKIMVFY>>&.
.vitem &$dnslist_domain$& &&&
&$dnslist_matched$& &&&
This variable contains the number of bytes in the longest line that was
received as part of the message, not counting the line termination
character(s).
-.new
It is not valid if the &%spool_files_wireformat%& option is used.
-.wen
.vitem &$message_age$&
.cindex "message" "age of"
separates the body from the header. Newlines are included in the count. See
also &$message_size$&, &$body_linecount$&, and &$body_zerocount$&.
-.new
If the spool file is wireformat
(see the &%spool_files_wireformat%& main option)
the CRLF line-terminators are included in the count.
-.wen
.vitem &$message_exim_id$&
.vindex "&$message_exim_id$&"
In the MAIL and RCPT ACLs, the value is zero because at that stage the
message has not yet been received.
-.new
This variable is not valid if the &%spool_files_wireformat%& option is used.
-.wen
.vitem &$message_size$&
.cindex "size" "of message"
space removed. Following the introduction of &$smtp_command$&, this variable is
somewhat redundant, but is retained for backwards compatibility.
-.new
.vitem &$smtp_command_history$&
.cindex SMTP "command history"
.vindex "&$smtp_command_history$&"
A comma-separated list (with no whitespace) of the most-recent SMTP commands
received, in time-order left to right. Only a limited number of commands
are remembered.
-.wen
.vitem &$smtp_count_at_connection_start$&
.vindex "&$smtp_count_at_connection_start$&"
is compiled with the content-scanning extension. For details, see section
&<<SECTscanspamass>>&.
+.new
+.vitem &$spf_header_comment$& &&&
+ &$spf_received$& &&&
+ &$spf_result$& &&&
+ &$spf_smtp_comment$&
+These variables are only available if Exim is built with SPF support.
+For details see section &<<SECSPF>>&.
+.wen
.vitem &$spool_directory$&
.vindex "&$spool_directory$&"
&%certextract%& expansion item, &%md5%&, &%sha1%& or &%sha256%& operator,
or a &%def%& condition.
+&*Note*&: Under current versions of OpenSSL, when a list of more than one
+file is used for &%tls_certificate%&, this variable is not reliable.
+
.vitem &$tls_in_peercert$&
.vindex "&$tls_in_peercert$&"
This variable refers to the certificate presented by the peer of an
This option defines the ACL that is run for each DKIM signature
(by default, or as specified in the dkim_verify_signers option)
of a received message.
-See chapter &<<CHAPdkim>>& for further details.
+See section &<<SECDKIMVFY>>& for further details.
.option acl_smtp_etrn main string&!! unset
.cindex "ETRN" "ACL for"
these hosts.
Hosts may use the BDAT command as an alternate to DATA.
-.new
.option commandline_checks_require_admin main boolean &`false`&
.cindex "restricting access to features"
This option restricts various basic checking features to require an
administrative user.
This affects most of the &%-b*%& options, such as &%-be%&.
-.wen
.option debug_store main boolean &`false`&
.cindex debugging "memory corruption"
This option gives a list of DKIM domains for which the DKIM ACL is run.
It is expanded after the message is received; by default it runs
the ACL once for each signature in the message.
-See chapter &<<CHAPdkim>>&.
+See section &<<SECDKIMVFY>>&.
.option dns_again_means_nonexist main "domain list&!!" unset
chapter &<<CHAPi18n>>& for details of Exim's support for internationalisation.
-.option spamd_address main string "see below"
+.option spamd_address main string "127.0.0.1 783"
This option is available when Exim is compiled with the content-scanning
extension. It specifies how Exim connects to SpamAssassin's &%spamd%& daemon.
-The default value is
-.code
-127.0.0.1 783
-.endd
See section &<<SECTscanspamass>>& for more details.
+.new
+.option spf_guess main string "v=spf1 a/24 mx/24 ptr ?all"
+This option is available when Exim is compiled with SPF support.
+See section &<<SECSPF>>& for more details.
+.wen
+
+
+
.option split_spool_directory main boolean false
.cindex "multiple spool directories"
.cindex "spool directory" "split"
By using this option to override the compiled-in path, it is possible to run
tests of Exim without using the standard spool.
-.new
.option spool_wireformat main boolean false
.cindex "spool directory" "file formats"
If this option is set, Exim may for some messages use an alternate format
Using any of the ACL conditions noted will negate the reception benefit
(as a Unix-mbox-format file is contructed for them).
The transimssion benefit is maintained.
-.wen
.option sqlite_lock_timeout main time 5s
.cindex "sqlite lookup type" "lock timeout"
is not required the &%tls_advertise_hosts%& option should be set empty.
-.option tls_certificate main string&!! unset
+.option tls_certificate main string list&!! unset
.cindex "TLS" "server certificate; location of"
.cindex "certificate" "server, location of"
-The value of this option is expanded, and must then be the absolute path to a
-file which contains the server's certificates. The server's private key is also
+The value of this option is expanded, and must then be a list of absolute paths to
+files which contains the server's certificates. Commonly only one file is
+needed.
+The server's private key is also
assumed to be in this file if &%tls_privatekey%& is unset. See chapter
&<<CHAPTLS>>& for further details.
use when sending messages as a client, you must set the &%tls_certificate%&
option in the relevant &(smtp)& transport.
+&*Note*&: If you use filenames based on IP addresses, change the list
+separator in the usual way to avoid confusion under IPv6.
+
+&*Note*&: Under current versions of OpenSSL, when a list of more than one
+file is used, the &$tls_in_ourcert$& veriable is unreliable.
+
+&*Note*&: OCSP stapling is not usable under OpenSSL
+when a list of more than one file is used.
+
If the option contains &$tls_out_sni$& and Exim is built against OpenSSL, then
if the OpenSSL build supports TLS extensions and the TLS client sends the
Server Name Indication extension, then this option and others documented in
.cindex "TLS" "server certificate revocation list"
.cindex "certificate" "revocation list for server"
This option specifies a certificate revocation list. The expanded value must
-be the name of a file that contains a CRL in PEM format.
+be the name of a file that contains CRLs in PEM format.
+
+.new
+Under OpenSSL the option can specify a directory with CRL files.
+
+&*Note:*& Under OpenSSL the option must, if given, supply a CRL
+for each signing element of the certificate chain (i.e. all but the leaf).
+For the file variant this can be multiple PEM blocks in the one file.
+.wen
See &<<SECTtlssni>>& for discussion of when this option might be re-expanded.
Usable for GnuTLS 3.4.4 or 3.3.17 or OpenSSL 1.1.0 (or later).
+.new
+For GnuTLS 3.5.6 or later the expanded value of this option can be a list
+of files, to match a list given for the &%tls_certificate%& option.
+The ordering of the two lists must match.
+.wen
+
.option tls_on_connect_ports main "string list" unset
.cindex SSMTP
-.option tls_privatekey main string&!! unset
+.option tls_privatekey main string list&!! unset
.cindex "TLS" "server private key; location of"
-The value of this option is expanded, and must then be the absolute path to a
-file which contains the server's private key. If this option is unset, or if
+The value of this option is expanded, and must then be a list of absolute paths to
+files which contains the server's private keys.
+If this option is unset, or if
the expansion is forced to fail, or the result is an empty string, the private
key is assumed to be in the same file as the server's certificates. See chapter
&<<CHAPTLS>>& for further details.
message on the same connection. See section &<<SECTmulmessam>>& for an
explanation of when this might be needed.
-.new
.option hosts_noproxy_tls smtp "host list&!!" *
.cindex "TLS" "passing connection"
.cindex "multiple SMTP deliveries"
the SMTP connection from and to the new process and any subsequents.
The new process has no access to TLS information, so cannot include it in
logging.
-.wen
(If an API is found to let OpenSSL be configured in this way,
let the Exim Maintainers know and we'll likely use it).
.next
+With GnuTLS, if an explicit list is used for the &%tls_privatekey%& main option
+main option, it must be ordered to match the &%tls_certificate%& list.
+.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
{HIGH:!MD5:!SHA1}}
.endd
+This example will prefer ECDSA-authenticated ciphers over RSA ones:
+.code
+tls_require_ciphers = ECDSA:RSA:!COMPLEMENTOFDEFAULT
+.endd
.section "Requiring specific ciphers or other parameters in GnuTLS" &&&
Further protection requires some further configuration at the server end.
-It is rumoured that all existing clients that support TLS/SSL use RSA
-encryption. To make this work you need to set, in the server,
+To make TLS work you need to set, in the server,
.code
tls_certificate = /some/file/name
tls_privatekey = /some/file/name
certificates that need to be sent to the client to enable it to authenticate
the server's certificate.
+For dual-stack (eg. RSA and ECDSA) configurations, these options can be
+colon-separated lists of file paths. Ciphers using given authentication
+algorithms require the presence of a suitable certificate to supply the
+public-key. The server selects among the certificates to present to the
+client depending on the selected cipher, hence the priority ordering for
+ciphers will affect which certificate is used.
+
If you do not understand about certificates and keys, please try to find a
source of this background information, which is not Exim-specific. (There are a
few comments below in section &<<SECTcerandall>>&.)
If the &%tls_verify_certificates%& option is set on the &(smtp)& transport, it
specifies a collection of expected server certificates.
-These may be the system default set (depending on library version),
-a file or,
-depending on library version, a directory,
-must name a file or,
-for OpenSSL only (not GnuTLS), a directory.
+These may be
+the system default set (depending on library version),
+a file,
+or (depending on library version) a directory.
The client verifies the server's certificate
against this collection, taking into account any revoked certificates that are
in the list defined by &%tls_crl%&.
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%&
.next
-.vindex "&%tls_ocsp_file%&"
&%tls_ocsp_file%&
.endlist
"SECTmulmessam"
.cindex "multiple SMTP deliveries with TLS"
.cindex "TLS" "multiple message deliveries"
-.new
Exim sends multiple messages down the same TCP/IP connection by starting up
an entirely new delivery process for each message, passing the socket from
one process to the next. This implementation does not fit well with the use
An older mode of operation can be enabled on a per-host basis by the
&%hosts_noproxy_tls%& option on the &(smtp)& transport. If the host matches
this list the proxy process descibed above is not used; instead Exim
-.wen
shuts down an existing TLS session being run by the delivery process
before passing the socket to a new process. The new process may then
try to start a new TLS session, and if successful, may try to re-authenticate
This ACL is evaluated before &%acl_smtp_mime%& and &%acl_smtp_data%&.
-For details on the operation of DKIM, see chapter &<<CHAPdkim>>&.
+For details on the operation of DKIM, see section &<<SECDKIM>>&.
.section "The SMTP MIME ACL" "SECID194"
.vitem &*queue*&&~=&~<&'text'&>
+.cindex "&%queue%& ACL modifier"
+.cindex "named queues" "selecting in ACL"
This modifier specifies the use of a named queue for spool files
for the message.
It can only be used before the message is received (i.e. not in
.vitem &*udpsend*&&~=&~<&'parameters'&>
+.cindex "UDP communications"
This modifier sends a UDP packet, for purposes such as statistics
collection or behaviour monitoring. The parameters are expanded, and
the result of the expansion must be a colon-separated list consisting
Note also that headers cannot be
modified by any of the post-data ACLs (DATA, MIME and DKIM).
Headers may be modified by routers (subject to the above) and transports.
-.new
The Received-By: header is generated as soon as the body reception starts,
rather than the traditional time after the full message is received;
this will affect the timestamp.
-.wen
All the usual ACLs are called; if one results in the message being
rejected, all effort spent in delivery (including the costs on
.cindex "disable DKIM verify"
.cindex "DKIM" "disable verify"
This control turns off DKIM verification processing entirely. For details on
-the operation and configuration of DKIM, see chapter &<<CHAPdkim>>&.
+the operation and configuration of DKIM, see section &<<SECDKIM>>&.
.vitem &*control&~=&~dscp/*&<&'value'&>
sender when checking recipients. If used indiscriminately, it reduces the
usefulness of callout caching.
-.new
.vitem &*hold*&
This option applies to recipient callouts only. For example:
.code
if the use_sender option is used,
if neither the random nor the use_postmaster option is used,
and if no other callouts intervene.
-.wen
.endlist
If you use any of the parameters that set a non-empty sender for the MAIL
item creates a signed address, and the &%prvscheck%& expansion item checks one.
The syntax of these expansion items is described in section
&<<SECTexpansionitems>>&.
+The validity period on signed addresses is seven days.
As an example, suppose the secret per-address keys are stored in an MySQL
database. A query to look up the key for an address could be defined as a macro
If the value of &%av_scanner%& starts with a dollar character, it is expanded
before use.
The usual list-parsing of the content (see &<<SECTlistconstruct>>&) applies.
-The following scanner types are supported in this release:
+The following scanner types are supported in this release,
+.new
+though individual ones can be included or not at build time:
+.wen
.vlist
.vitem &%avast%&
to be scanned, which will should normally result in less I/O happening and be
more efficient. Normally in the TCP case, the data is streamed to ClamAV as
Exim does not assume that there is a common filesystem with the remote host.
-There is an option WITH_OLD_CLAMAV_STREAM in &_src/EDITME_& available, should
-you be running a version of ClamAV prior to 0.95.
The final example shows that multiple TCP targets can be specified. Exim will
randomly use one for each incoming email (i.e. it load balances them). Note
.endd
If you omit the argument, the default values show above are used.
-.new
.vitem &%f-prot6d%&
.cindex "virus scanners" "f-prot6d"
The f-prot6d scanner is accessed using the FPSCAND protocol over TCP.
av_scanner = f-prot6d:localhost 10200
.endd
If you omit the argument, the default values show above are used.
-.wen
.vitem &%fsecure%&
.cindex "virus scanners" "F-Secure"
.code
av_scanner = sock:127.0.0.1 6001:%s:(SPAM|VIRUS):(.*)$
.endd
-.new
Note that surrounding whitespace is stripped from each option, meaning
there is no way to specify a trailing newline.
The socket specifier and both regular-expressions are required.
Default for the commandline is &_%s\n_& (note this does have a trailing newline);
specify an empty element to get this.
-.wen
.vitem &%sophie%&
.cindex "virus scanners" "Sophos and Sophie"
.vlist
.vitem &*int&~body_linecount*&
This variable contains the number of lines in the message's body.
-.new
It is not valid if the &%spool_files_wireformat%& option is used.
-.wen
.vitem &*int&~body_zerocount*&
This variable contains the number of binary zero bytes in the message's body.
-.new
It is not valid if the &%spool_files_wireformat%& option is used.
-.wen
.vitem &*unsigned&~int&~debug_selector*&
This variable is set to zero when no debugging is taking place. Otherwise, it
flagged with &`->`& instead of &`=>`&. When two or more messages are delivered
down a single SMTP connection, an asterisk follows the IP address in the log
lines for the second and subsequent messages.
-.new
When two or more messages are delivered down a single TLS connection, the
DNS and some TLS-related information logged for the first message delivered
will not be present in the log lines for the second and subsequent messages.
TLS cipher information is still available.
-.wen
.cindex "delivery" "cutthrough; logging"
.cindex "cutthrough" "logging"
&` `& command list for &"no mail in SMTP session"&
&`CV `& certificate verification status
&`D `& duration of &"no mail in SMTP session"&
+&`DKIM`& domain verified in incoming message
&`DN `& distinguished name from peer certificate
&`DS `& DNSSEC secured lookups
&`DT `& on &`=>`& lines: time taken for a delivery
&` `& on &"Completed"& lines: time spent on queue
&`R `& on &`<=`& lines: reference for local bounce
&` `& on &`=>`& &`>>`& &`**`& and &`==`& lines: router name
+&`RT `& on &`<=`& lines: time taken for reception
&`S `& size of message in bytes
&`SNI `& server name indication from TLS client hello
&`ST `& shadow transport name
.endd
failed. The delivery was discarded.
.endlist olist
+.next
+.new
+.cindex DKIM "log line"
+&'DKIM: d='&&~&~Verbose results of a DKIM verification attempt, if enabled for
+logging and the message has a DKIM signature header.
+.wen
.endlist ilist
&`*delay_delivery `& immediate delivery delayed
&` deliver_time `& time taken to perform delivery
&` delivery_size `& add &`S=`&&'nnn'& to => lines
+&`*dkim `& DKIM verified domain on <= lines
+&` dkim_verbose `& separate full DKIM verification result line, per signature
&`*dnslist_defer `& defers of DNS list (aka RBL) lookups
&` dnssec `& DNSSEC secured lookups
&`*etrn `& ETRN commands
&` incoming_interface `& local interface on <= and => lines
&` incoming_port `& remote port on <= lines
&`*lost_incoming_connection `& as it says (includes timeouts)
-&` millisec `& millisecond timestamps and QT,DT,D times
+&` millisec `& millisecond timestamps and RT,QT,DT,D times
&` outgoing_interface `& local interface on => lines
&` outgoing_port `& add remote port to => lines
&`*queue_run `& start and end queue runs
&%deliver_time%&: For each delivery, the amount of real time it has taken to
perform the actual delivery is logged as DT=<&'time'&>, for example, &`DT=1s`&.
If millisecond logging is enabled, short times will be shown with greater
-precision, eg. &`DT=0.304`&.
+precision, eg. &`DT=0.304s`&.
.next
.cindex "log" "message size on delivery"
.cindex "size" "of message"
&%delivery_size%&: For each delivery, the size of message delivered is added to
the &"=>"& line, tagged with S=.
.next
+.new
+.cindex log "DKIM verification"
+.cindex DKIM "verification logging"
+&%dkim%&: For message acceptance log lines, when an DKIM signture in the header
+verifies successfully a tag of DKIM is added, with one of the verified domains.
+.next
+.cindex log "DKIM verification"
+.cindex DKIM "verification logging"
+&%dkim_verbose%&: A log entry is written for each attempted DKIM verification.
+.wen
+.next
.cindex "log" "dnslist defer"
.cindex "DNS list" "logging defer"
.cindex "black list (DNS)"
&%lost_incoming_connection%&: A log line is written when an incoming SMTP
connection is unexpectedly dropped.
.next
-.new
.cindex "log" "millisecond timestamps"
.cindex millisecond logging
.cindex timstamps "millisecond, in logs"
&%millisec%&: Timestamps have a period and three decimal places of finer granularity
appended to the seconds value.
-.wen
.next
.cindex "log" "outgoing interface"
.cindex "log" "local interface"
the local host is logged as QT=<&'time'&> on &"Completed"& lines, for
example, &`QT=3m45s`&. The clock starts when Exim starts to receive the
message, so it includes reception time as well as the total delivery time.
+.new
+.next
+.cindex "log" "receive duration"
+&%receive_time%&: For each message, the amount of real time it has taken to
+perform the reception is logged as RT=<&'time'&>, for example, &`RT=1s`&.
+If millisecond logging is enabled, short times will be shown with greater
+precision, eg. &`RT=0.204s`&.
+.wen
.next
.cindex "log" "recipients"
&%received_recipients%&: The recipients of a message are listed in the main log
unprivileged), Exim must be built to allow group read access to its spool
files.
-.new
By default, regular users are trusted to perform basic testing and
introspection commands, as themselves. This setting can be tightened by
setting the &%commandline_checks_require_admin%& option.
This affects most of the checking options,
such as &%-be%& and anything else &%-b*%&.
-.wen
.section "Spool files" "SECID275"
-J file and uses it to update the -H file before starting the next delivery
attempt.
-.new
Files whose names end with -K or .eml may also be seen in the spool.
These are temporaries used for DKIM or malware processing, when that is used.
They should be tidied up by normal operations; any old ones are probably
relics of crashes and can be removed.
-.wen
.section "Format of the -H file" "SECID282"
.cindex "uid (user id)" "in spool file"
If a message was scanned by SpamAssassin, this is present. It records the value
of &$spam_score_int$&.
-.new
.vitem &%-spool_file_wireformat%&
The -D file for this message is in wire-format (for ESMTP CHUNKING)
rather than Unix-format.
The line-ending is CRLF rather than newline.
There is still, however, no leading-dot-stuffing.
-.wen
.vitem &%-tls_certificate_verified%&
A TLS certificate was received from the client that sent this message, and the
.ecindex IIDforspo2
.ecindex IIDforspo3
-.new
.section "Format of the -D file" "SECID282a"
The data file is traditionally in Unix-standard format: lines are ended with
an ASCII newline character.
ESMTP CHUNKING option, meaning lower processing overhead.
Lines are terminated with an ASCII CRLF pair.
There is no dot-stuffing (and no dot-termination).
-.wen
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
-.chapter "Support for DKIM (DomainKeys Identified Mail)" "CHAPdkim" &&&
- "DKIM Support"
+.chapter "DKIM and SPF" "CHAPdkim" &&&
+ "DKIM and SPF Support"
.cindex "DKIM"
+.section "DKIM (DomainKeys Identified Mail)" SECDKIM
+
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.
+.new
+As DKIM relies on the message being unchanged in transit, messages handled
+by a mailing-list (which traditionally adds to the message) will not match
+any original DKIM signature.
+.wen
+
DKIM support is compiled into Exim by default if TLS support is present.
It can be disabled by setting DISABLE_DKIM=yes in &_Local/Makefile_&.
default "policy". Instead it enables you to build your own policy using
Exim's standard controls.
+.new
Please note that verification of DKIM signatures in incoming mail is turned
-on by default for logging purposes. For each signature in incoming email,
+on by default for logging (in the <= line) purposes.
+
+Additional log detail can be enabled using the &%dkim_verbose%& log_selector.
+When set, 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 (with line-breaks added for clarity):
.code
c=relaxed/relaxed a=rsa-sha1
i=@facebookmail.com t=1252484542 [verification succeeded]
.endd
+.wen
+
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
control modifier. This should typically be done in the RCPT ACL, at points
.section "Signing outgoing messages" "SECDKIMSIGN"
.cindex "DKIM" "signing"
+.new
+For signing to be usable you must have published a DKIM record in DNS.
+Note that RFC 8301 says:
+.code
+rsa-sha1 MUST NOT be used for signing or verifying.
+
+Signers MUST use RSA keys of at least 1024 bits for all keys.
+Signers SHOULD use RSA keys of at least 2048 bits.
+.endd
+.wen
+.wen
+
Signing is enabled by setting private options on the SMTP transport.
These options take (expandable) strings as arguments.
.option dkim_domain smtp string list&!! unset
The domain(s) you want to sign with.
-.new
After expansion, this can be a list.
Each element in turn is put into the &%$dkim_domain%& expansion variable
while expanding the remaining signing options.
-.wen
-If it is empty after expansion, DKIM signing is not done.
+If it is empty after expansion, DKIM signing is not done,
+and no error will result even if &%dkim_strict%& is set.
.option dkim_selector smtp string list&!! unset
This sets the key selector string.
-.new
After expansion, which can use &$dkim_domain$&, this can be a list.
Each element in turn is put in the expansion
variable &%$dkim_selector%& which may be used in the &%dkim_private_key%&
option along with &%$dkim_domain%&.
-If the option is empty after expansion, DKIM signing is not done for this domain.
-.wen
+If the option is empty after expansion, DKIM signing is not done for this domain,
+and no error will result even if &%dkim_strict%& is set.
.option dkim_private_key smtp string&!! unset
This sets the private key to use.
be signed. This case will not result in an error, even if &%dkim_strict%&
is set.
.endlist
-If the option is empty after expansion, DKIM signing is not done.
.new
+Note that RFC 8301 says:
+.code
+Signers MUST use RSA keys of at least 1024 bits for all keys.
+Signers SHOULD use RSA keys of at least 2048 bits.
+.endd
+.wen
+
.option dkim_hash smtp string&!! sha256
Can be set alternatively to &"sha1"& to use an alternate hash
-method. Note that sha1 is now condidered insecure, and deprecated.
+method.
+
+.new
+Note that RFC 8301 says:
+.code
+rsa-sha1 MUST NOT be used for signing or verifying.
+.endd
+.wen
.option dkim_identity smtp string&!! unset
If set after expansion, the value is used to set an "i=" tag in
syntax of this optional tag to a mail address, with possibly-empty
local part, an @, and a domain identical to or subdomain of the "d="
tag value. Note that Exim does not check the value.
-.wen
.option dkim_canon smtp string&!! unset
This option sets the canonicalization method used when signing a message.
.option dkim_sign_headers smtp string&!! "see below"
If set, this option must expand to a colon-separated
list of header names.
-.new
Headers with these names, or the absence or such a header, will be included
in the message signature.
When unspecified, the header names listed in RFC4871 will be used,
If a '+' prefix if used, all headers that are present with this name
will be signed, and one signtature added for a missing header with the
name will be appended.
-.wen
-.section "Verifying DKIM signatures in incoming mail" "SECID514"
+.section "Verifying DKIM signatures in incoming mail" "SECDKIMVFY"
.cindex "DKIM" "verification"
Verification of DKIM signatures in SMTP incoming email is implemented via the
If a domain or identity is listed several times in the (expanded) value of
&%dkim_verify_signers%&, the ACL is only called once for that domain or identity.
+If multiple signatures match a domain (or identity), the ACL is called once
+for each matching signature.
+
Inside the &%acl_smtp_dkim%&, the following expansion variables are
available (from most to least important):
&%dkim_verify_signers%& (see above).
.vitem &%$dkim_verify_status%&
-A string describing the general status of the signature. One of
+Within the DKIM ACL,
+a string describing the general status of the signature. One of
.ilist
&%none%&: There is no signature in the message for the current domain or
identity (as reflected by &%$dkim_cur_signer%&).
&%pass%&: The signature passed verification. It is valid.
.endlist
+This variable can be overwritten using an ACL 'set' modifier.
+This might, for instance, be done to enforce a policy restriction on
+hash-method or key-size:
+.code
+ warn condition = ${if eq {$dkim_algo}{rsa-sha1}}
+ condition = ${if eq {$dkim_verify_status}{pass}}
+ logwrite = NOTE: forcing dkim verify fail (was pass)
+ set dkim_verify_status = fail
+ set dkim_verify_reason = hash too weak
+.endd
+
+After all the DKIM ACL runs have completed, the value becomes a
+colon-separated list of the values after each run.
+
.vitem &%$dkim_verify_reason%&
A string giving a little bit more detail when &%$dkim_verify_status%& is either
"fail" or "invalid". One of
DKIM verification. It may of course also mean that the signature is forged.
.endlist
+This variable can be overwritten, with any value, using an ACL 'set' modifier.
+
.vitem &%$dkim_domain%&
The signing domain. IMPORTANT: This variable is only populated if there is
an actual signature in the message for the current domain or identity (as
.vitem &%$dkim_algo%&
The algorithm used. One of 'rsa-sha1' or 'rsa-sha256'.
+.new
+Note that RFC 8301 says:
+.code
+rsa-sha1 MUST NOT be used for signing or verifying.
+
+DKIM signatures identified as having been signed with historic
+algorithms (currently, rsa-sha1) have permanently failed evaluation
+.endd
+
+To enforce this you must have a DKIM ACL which checks this variable
+and overwrites the &$dkim_verify_status$& variable as discussed above.
+.wen
+
.vitem &%$dkim_canon_body%&
The body canonicalization method. One of 'relaxed' or 'simple'.
.vitem &%$dkim_key_length%&
Number of bits in the key.
+
+.new
+Note that RFC 8301 says:
+.code
+Verifiers MUST NOT consider signatures using RSA keys of
+less than 1024 bits as valid signatures.
+.endd
+
+To enforce this you must have a DKIM ACL which checks this variable
+and overwrites the &$dkim_verify_status$& variable as discussed above.
+.wen
+
.endlist
In addition, two ACL conditions are provided:
for more information of what they mean.
.endlist
+
+
+
+.new
+.section "SPF (Sender Policy Framework)" SECSPF
+.cindex SPF verification
+
+SPF is a mechanism whereby a domain may assert which IP addresses may transmit
+messages with its domain in the envelope from, documented by RFC 7208.
+For more information on SPF see &url(http://www.openspf.org).
+
+Messages sent by a system not authorised will fail checking of such assertions.
+This includes retransmissions done by traditional forwarders.
+
+SPF verification support is built into Exim if SUPPORT_SPF=yes is set in
+&_Local/Makefile_&. The support uses the &_libspf2_& library
+&url(http://www.libspf2.org/).
+There is no Exim involvement on the trasmission of messages; publishing certain
+DNS records is all that is required.
+
+For verification, an ACL condition and an expansion lookup are provided.
+
+.cindex SPF "ACL condition"
+.cindex ACL "spf condition"
+The ACL condition "spf" can be used at or after the MAIL ACL.
+It takes as an argument a list of strings giving the outcome of the SPF check,
+and will succeed for any matching outcome.
+Valid strings are:
+.vlist
+.vitem &%pass%&
+The SPF check passed, the sending host is positively verified by SPF.
+
+.vitem &%fail%&
+The SPF check failed, the sending host is NOT allowed to send mail for the
+domain in the envelope-from address.
+
+.vitem &%softfail%&
+The SPF check failed, but the queried domain can't absolutely confirm that this
+is a forgery.
+
+.vitem &%none%&
+The queried domain does not publish SPF records.
+
+.vitem &%neutral%&
+The SPF check returned a "neutral" state. This means the queried domain has
+published a SPF record, but wants to allow outside servers to send mail under
+its domain as well. This should be treated like "none".
+
+.vitem &%permerror%&
+This indicates a syntax error in the SPF record of the queried domain.
+You may deny messages when this occurs. (Changed in 4.83)
+
+.vitem &%temperror%&
+This indicates a temporary error during all processing, including Exim's
+SPF processing. You may defer messages when this occurs.
+(Changed in 4.83)
+
+.vitem &%err_temp%&
+Same as permerror, deprecated in 4.83, will be removed in a future release.
+
+.vitem &%err_perm%&
+Same as temperror, deprecated in 4.83, will be removed in a future release.
+.endlist
+
+You can prefix each string with an exclamation mark to invert
+its meaning, for example "!fail" will match all results but
+"fail". The string list is evaluated left-to-right, in a
+short-circuit fashion.
+
+Example:
+.code
+deny spf = fail
+ message = $sender_host_address is not allowed to send mail from \
+ ${if def:sender_address_domain \
+ {$sender_address_domain}{$sender_helo_name}}. \
+ Please see http://www.openspf.org/Why?scope=\
+ ${if def:sender_address_domain {mfrom}{helo}};\
+ identity=${if def:sender_address_domain \
+ {$sender_address}{$sender_helo_name}};\
+ ip=$sender_host_address
+.endd
+
+When the spf condition has run, it sets up several expansion
+variables:
+
+.cindex SPF "verification variables"
+.vlist
+.vitem &$spf_header_comment$&
+.vindex &$spf_header_comment$&
+ This contains a human-readable string describing the outcome
+ of the SPF check. You can add it to a custom header or use
+ it for logging purposes.
+
+.vitem &$spf_received$&
+.vindex &$spf_received$&
+ This contains a complete Received-SPF: header that can be
+ added to the message. Please note that according to the SPF
+ draft, this header must be added at the top of the header
+ list. Please see section 10 on how you can do this.
+
+ Note: in case of "Best-guess" (see below), the convention is
+ to put this string in a header called X-SPF-Guess: instead.
+
+.vitem &$spf_result$&
+.vindex &$spf_result$&
+ This contains the outcome of the SPF check in string form,
+ one of pass, fail, softfail, none, neutral, permerror or
+ temperror.
+
+.vitem &$spf_smtp_comment$&
+.vindex &$spf_smtp_comment$&
+ This contains a string that can be used in a SMTP response
+ to the calling party. Useful for "fail".
+.endlist
+
+
+.cindex SPF "ACL condition"
+.cindex ACL "spf_guess condition"
+.cindex SPF "best guess"
+In addition to SPF, you can also perform checks for so-called
+"Best-guess". Strictly speaking, "Best-guess" is not standard
+SPF, but it is supported by the same framework that enables SPF
+capability.
+Refer to &url(http://www.openspf.org/FAQ/Best_guess_record)
+for a description of what it means.
+
+To access this feature, simply use the spf_guess condition in place
+of the spf one. For example:
+
+.code
+deny spf_guess = fail
+ message = $sender_host_address doesn't look trustworthy to me
+.endd
+
+In case you decide to reject messages based on this check, you
+should note that although it uses the same framework, "Best-guess"
+is not SPF, and therefore you should not mention SPF at all in your
+reject message.
+
+When the spf_guess condition has run, it sets up the same expansion
+variables as when spf condition is run, described above.
+
+Additionally, since Best-guess is not standardized, you may redefine
+what "Best-guess" means to you by redefining the main configuration
+&%spf_guess%& option.
+For example, the following:
+
+.code
+spf_guess = v=spf1 a/16 mx/16 ptr ?all
+.endd
+
+would relax host matching rules to a broader network range.
+
+
+.cindex SPF "lookup expansion"
+.cindex lookup spf
+A lookup expansion is also available. It takes an email
+address as the key and an IP address as the database:
+
+.code
+ ${lookup {username@domain} spf {ip.ip.ip.ip}}
+.endd
+
+The lookup will return the same result strings as they can appear in
+&$spf_result$& (pass,fail,softfail,neutral,none,err_perm,err_temp).
+Currently, only IPv4 addresses are supported.
+
+
+. wen-for SPF section
+.wen
+
+
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
before or after the action is associates with. Those which fire before
can be used to affect that action (more on this below).
-.new
The third column in the table above says what section of the configumration
should define the event action.
-.wen
An additional variable, &$event_data$&, is filled with information varying
with the event type:
git://git.exim.org / users / heiko / exim.git / blobdiff