.set I " "
.macro copyyear
-2012
+2013
.endmacro
. /////////////////////////////////////////////////////////////////////////////
<author><firstname>Exim</firstname><surname>Maintainers</surname></author>
<authorinitials>EM</authorinitials>
<revhistory><revision>
- <revnumber>
-.version
- </revnumber>
- <date>
-.fulldate
- </date>
+.versiondatexml
<authorinitials>EM</authorinitials>
</revision></revhistory>
<copyright><year>
.cindex "distribution" "signing details"
.cindex "distribution" "public key"
.cindex "public key for signed distribution"
-.new
The distributions will be PGP signed by an individual key of the Release
Coordinator. This key will have a uid containing an email address in the
&'exim.org'& domain and will have signatures from other people, including
key &'0x403043153903637F'&, although that key is expected to be replaced in 2013.
A trust path from Nigel's key to Phil's can be observed at
&url(https://www.security.spodhuis.org/exim-trustpath).
+
+.new
+Releases have also been authorized to be performed by Todd Lyons who signs with
+key &'0xC4F4F94804D29EBA'&. A direct trust path exists between previous RE Phil
+Pennock and Todd Lyons through a common associate.
.wen
The signatures for the tar bundles are in:
.cindex "incorporated code"
.cindex "regular expressions" "library"
.cindex "PCRE"
+.cindex "OpenDMARC"
A number of pieces of external code are included in the Exim distribution.
.ilist
SOFTWARE.
.endblockquote
+.next
+.new
+.cindex "opendmarc" "acknowledgment"
+The DMARC implementation uses the OpenDMARC library which is Copyrighted by
+The Trusted Domain Project. Portions of Exim source which use OpenDMARC
+derived code are indicated in the respective source files. The full OpenDMARC
+license is provided in the LICENSE.opendmarc file contained in the distributed
+source code.
+.wen
+
.next
Many people have contributed code fragments, some large, some small, that were
not covered by any specific licence requirements. It is assumed that the
&%verify_recipient%&, which independently control the use of the router for
sender and recipient verification. You can set these options directly if
you want a router to be used for only one type of verification.
-Note that cutthrough delivery is classed as a recipient verification
-for this purpose.
+.new "Note that cutthrough delivery is classed as a recipient verification for this purpose."
.next
If the &%address_test%& option is set false, the router is skipped when Exim is
run with the &%-bt%& option to test an address routing. This can be helpful
.next
Routers can be designated for use only when verifying an address, as
opposed to routing it for delivery. The &%verify_only%& option controls this.
-Again, cutthrough delibery counts as a verification.
+.new "Again, cutthrough delivery counts as a verification."
.next
Individual routers can be explicitly skipped when running the routers to
check an address given in the SMTP EXPN command (see the &%expn%& option).
the message, and applies to any subsequent delivery attempts that may happen
for that message.
+.new
.vitem &%-n%&
.oindex "&%-n%&"
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.
+.wen
.vitem &%-O%&&~<&'data'&>
.oindex "&%-O%&"
It sets the incoming protocol and host name (for trusted callers). The
host name and its colon can be omitted when only the protocol is to be set.
Note the Exim already has two private options, &%-pd%& and &%-ps%&, that refer
-to embedded Perl. It is therefore impossible to set a protocol value of &`p`&
+to embedded Perl. It is therefore impossible to set a protocol value of &`d`&
or &`s`& using this option (but that does not seem a real limitation).
.vitem &%-q%&
The authorization code can be &"Y"& for yes, &"N"& for no, &"X"& for explicit
authorization required but absent, or &"?"& for unknown.
+.new
.cindex "A+" "in &(dnsdb)& lookup"
The pseudo-type A+ performs an A6 lookup (if configured) followed by an AAAA
and then an A lookup. All results are returned; defer processing
.code
${lookup dnsdb {>; a+=$sender_helo_name}}
.endd
+.wen
.section "Multiple dnsdb lookups" "SECID67"
.cindex "&`+include_unknown`&"
.cindex "&`+ignore_unknown`&"
-By default, Exim behaves as if the host does not match the list. This may not
-always be what you want to happen. To change Exim's behaviour, the special
-items &`+include_unknown`& or &`+ignore_unknown`& may appear in the list (at
-top level &-- they are not recognized in an indirected file).
+Exim parses a host list from left to right. If it encounters a permanent
+lookup failure in any item in the host list before it has found a match,
+Exim treats it as a failure and the default behavior is as if the host
+does not match the list. This may not always be what you want to happen.
+To change Exim's behaviour, the special items &`+include_unknown`& or
+&`+ignore_unknown`& may appear in the list (at top level &-- they are
+not recognized in an indirected file).
.ilist
If any item that follows &`+include_unknown`& requires information that
list. The effect of each one lasts until the next, or until the end of the
list.
+.new
+To explain the host/ip processing logic a different way for the same ACL:
+
+.ilist
+If you have name lookups or wildcarded host names and
+IP addresses in the same host list, you should normally put the IP
+addresses first. For example, in an ACL you could have:
+.code
+accept hosts = 10.9.8.7 : *.friend.example
+.endd
+The reason you normally would order it this way lies in the
+left-to-right way that Exim processes lists. It can test IP addresses
+without doing any DNS lookups, but when it reaches an item that requires
+a host name, it fails if it cannot find a host name to compare with the
+pattern. If the above list is given in the opposite order, the
+&%accept%& statement fails for a host whose name cannot be found, even
+if its IP address is 10.9.8.7.
+
+.next
+If you really do want to do the name check first, and still recognize the IP
+address, you can rewrite the ACL like this:
+.code
+accept hosts = *.friend.example
+accept hosts = 10.9.8.7
+.endd
+If the first &%accept%& fails, Exim goes on to try the second one. See chapter
+&<<CHAPACL>>& for details of ACLs. Alternatively, you can use
+&`+ignore_unknown`&, which was discussed in depth in the first example in
+this section.
+.endlist
+.wen
+
+
.section "Temporary DNS errors when looking up host information" &&&
"SECTtemdnserr"
expansion item below.
+.new
.vitem "&*${acl{*&<&'name'&>&*}{*&<&'arg'&>&*}...}*&"
.cindex "expansion" "calling an acl"
.cindex "&%acl%&" "call from expansion"
If no message is set and the ACL returns accept or deny
the expansion result is an empty string.
If the ACL returns defer the result is a forced-fail. Otherwise the expansion fails.
+.wen
.vitem "&*${dlfunc{*&<&'file'&>&*}{*&<&'function'&>&*}{*&<&'arg'&>&*}&&&
command does not succeed. If both strings are omitted, the result is contents
of the standard output/error on success, and nothing on failure.
+.new
.vindex "&$run_in_acl$&"
The standard output/error of the command is put in the variable &$value$&.
In this ACL example, the output of a command is logged for the admin to
.code
${run{/bin/bash -c "/usr/bin/id >/tmp/id"}{yes}{yes}}
.endd
+.wen
.vindex "&$runrc$&"
The return code from the command is put in the variable &$runrc$&, and this
address. See the &*filter*&, &*map*&, and &*reduce*& items for ways of
processing lists.
+.new
+To clarify "list of addresses in RFC 2822 format" mentioned above, Exim follows
+a strict interpretation of header line formatting. Exim parses the bare,
+unquoted portion of an email address and if it finds a comma, treats it as an
+email address seperator. For the example header line:
+.code
+From: =?iso-8859-2?Q?Last=2C_First?= <user@example.com>
+.endd
+The first example below demonstrates that Q-encoded email addresses are parsed
+properly if it is given the raw header (in this example, &`$rheader_from:`&).
+It does not see the comma because it's still encoded as "=2C". The second
+example below is passed the contents of &`$header_from:`&, meaning it gets
+de-mimed. Exim sees the decoded "," so it treats it as &*two*& email addresses.
+The third example shows that the presence of a comma is skipped when it is
+quoted.
+.code
+# exim -be '${addresses:From: \
+=?iso-8859-2?Q?Last=2C_First?= <user@example.com>}'
+user@example.com
+# exim -be '${addresses:From: Last, First <user@example.com>}'
+Last:user@example.com
+# exim -be '${addresses:From: "Last, First" <user@example.com>}'
+user@example.com
+.endd
+.wen
.vitem &*${base62:*&<&'digits'&>&*}*&
.cindex "&%base62%& expansion item"
be useful for processing the output of the MD5 and SHA-1 hashing functions.
+
+.new
+.vitem &*${hexquote:*&<&'string'&>&*}*&
+.cindex "quoting" "hex-encoded unprintable characters"
+.cindex "&%hexquote%& expansion item"
+This operator converts non-printable characters in a string into a hex
+escape form. Byte values between 33 (!) and 126 (~) inclusive are left
+as is, and other byte values are converted to &`\xNN`&, for example a
+byte value 127 is converted to &`\x7f`&.
+.wen
+
+
.vitem &*${lc:*&<&'string'&>&*}*&
.cindex "case forcing in strings"
.cindex "string" "case forcing"
when &%length%& is used as an operator.
+.new
.vitem &*${listcount:*&<&'string'&>&*}*&
.cindex "expansion" "list item count"
.cindex "list" "item count"
The string is interpreted as a list and the number of items is returned.
-.vitem &*${listnamed:*&<&'name'&>&*}*&&~and&~&*${list_*&<&'type'&>&*name*&>&*}*&
+.vitem &*${listnamed:*&<&'name'&>&*}*&&~and&~&*${listnamed_*&<&'type'&>&*:*&<&'name'&>&*}*&
.cindex "expansion" "named list"
.cindex "&%listnamed%& expansion item"
The name is interpreted as a named list and the content of the list is returned,
expanding any referenced lists, re-quoting as needed for colon-separation.
-If the optional type if given it must be one of "a", "d", "h" or "l"
+If the optional type is given it must be one of "a", "d", "h" or "l"
and selects address-, domain-, host- or localpart- lists to search among respectively.
Otherwise all types are searched in an undefined order and the first
matching list is returned.
+.wen
.vitem &*${local_part:*&<&'string'&>&*}*&
10M, not if 10M is larger than &$message_size$&.
+.new
.vitem &*acl&~{{*&<&'name'&>&*}{*&<&'arg1'&>&*}&&&
{*&<&'arg2'&>&*}...}*&
.cindex "expansion" "calling an acl"
the result of the expansion, otherwise it is empty.
If the ACL returns accept the condition is true; if deny, false.
If the ACL returns defer the result is a forced-fail.
+.wen
.vitem &*bool&~{*&<&'string'&>&*}*&
.cindex "expansion" "boolean parsing"
The value of &$item$& is saved and restored while &*forany*& or &*forall*& is
being processed, to enable these expansion items to be nested.
+.new "To scan a named list, expand it with the &*listnamed*& operator."
+
.vitem &*ge&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& &&&
&*gei&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*&
process. However, a trusted user can override this by means of the &%-oMai%&
command line option.
-
+.new
+.vitem &$authenticated_fail_id$&
+.cindex "authentication" "fail" "id"
+.vindex "&$authenticated_fail_id$&"
+When an authentication attempt fails, the variable &$authenticated_fail_id$&
+will contain the failed authentication id. If more than one authentication
+id is attempted, it will contain only the last one. The variable is
+available for processing in the ACL's, generally the quit or notquit ACL.
+A message to a local recipient could still be accepted without requiring
+authentication, which means this variable could also be visible in all of
+the ACL's as well.
+.wen
.vitem &$authenticated_sender$&
be terminated by colon or white space, because it may contain a wide variety of
characters. Note also that braces must &'not'& be used.
+.new
.vitem &$headers_added$&
.vindex "&$headers_added$&"
Within an ACL this variable contains the headers added so far by
the ACL modifier add_header (section &<<SECTaddheadacl>>&).
The headers are a newline-separated list.
+.wen
.vitem &$home$&
.vindex "&$home$&"
.vindex "&$return_size_limit$&"
This is an obsolete name for &$bounce_return_size_limit$&.
+.new
+.vitem &$router_name$&
+.cindex "router" "name"
+.cindex "name" "of router"
+.vindex "&$router_name$&"
+During the running of a router this variable contains its name.
+.wen
+
.vitem &$runrc$&
.cindex "return code" "from &%run%& expansion"
.vindex "&$runrc$&"
command, which can be found in the separate document entitled &'Exim's
interfaces to mail filtering'&.
+.new
.vitem &$tls_in_bits$&
.vindex "&$tls_in_bits$&"
Contains an approximation of the TLS cipher's bit-strength
During outbound
SMTP deliveries, this variable reflects the value of the &%tls_sni%& option on
the transport.
+.wen
.vitem &$tod_bsdinbox$&
.vindex "&$tod_bsdinbox$&"
This variable contains the UTC date and time in &"Zulu"& format, as specified
by ISO 8601, for example: 20030221154023Z.
+.new
+.vitem &$transport_name$&
+.cindex "transport" "name"
+.cindex "name" "of transport"
+.vindex "&$transport_name$&"
+During the running of a transport, this variable contains its name.
+.wen
+
.vitem &$value$&
.vindex "&$value$&"
This variable contains the result of an expansion lookup, extraction operation,
.section "TLS" "SECID108"
.table2
.row &%gnutls_compat_mode%& "use GnuTLS compatibility mode"
-.row &%gnutls_enable_pkcs11%& "allow GnuTLS to autoload PKCS11 modules"
+.row &%gnutls_allow_auto_pkcs11%& "allow GnuTLS to autoload PKCS11 modules"
.row &%openssl_options%& "adjust OpenSSL compatibility options"
.row &%tls_advertise_hosts%& "advertise TLS to these hosts"
.row &%tls_certificate%& "location of server certificate"
&url(http://cr.yp.to/smtp/8bitmime.html)
.endd
+.new
To log received 8BITMIME status use
.code
log_selector = +8bitmime
.endd
+.wen
.option acl_not_smtp main string&!! unset
.cindex "&ACL;" "for non-SMTP messages"
.new
-option gnutls_enable_pkcs11 main boolean unset
+option gnutls_allow_auto_pkcs11 main boolean unset
This option will let GnuTLS (2.12.0 or later) autoload PKCS11 modules with
the p11-kit configuration files in &_/etc/pkcs11/modules/_&.
See
-&url(http://www.gnu.org/software/gnutls/manual/gnutls.html#Smart-cards-and-HSMs)
+&url(http://www.gnutls.org/manual/gnutls.html#Smart-cards-and-HSMs)
for documentation.
.wen
.next
&`no_tlsv1_2`&
.next
+.new
+&`safari_ecdhe_ecdsa_bug`&
+.wen
+.next
&`single_dh_use`&
.next
&`single_ecdh_use`&
&`tls_rollback_bug`&
.endlist
+.new
+As an aside, the &`safari_ecdhe_ecdsa_bug`& item is a misnomer and affects
+all clients connecting using the MacOS SecureTransport TLS facility prior
+to MacOS 10.8.4, including email clients. If you see old MacOS clients failing
+to negotiate TLS then this option value might help, provided that your OpenSSL
+release is new enough to contain this work-around. This may be a situation
+where you have to upgrade OpenSSL to get buggy clients working.
+.wen
+
.option oracle_servers main "string list" unset
.cindex "Oracle" "server list"
. Allow this long option name to split; give it unsplit as a fifth argument
. for the automatic .oindex that is generated by .option.
+. We insert " &~&~" which is both pretty nasty visually and results in
+. non-searchable text. HowItWorks.txt mentions an option for inserting
+. zero-width-space, which would be nicer visually and results in (at least)
+. html that Firefox will split on when it's forced to reflow (rather than
+. inserting a horizontal scrollbar). However, the text is still not
+. searchable. NM changed this occurrence for bug 1197 to no longer allow
+. the option name to split.
.option "smtp_accept_max_per_connection" main integer 1000 &&&
smtp_accept_max_per_connection
various &%-od%&&'x'& command line options.
-. Allow this long option name to split; give it unsplit as a fifth argument
-. for the automatic .oindex that is generated by .option.
+. See the comment on smtp_accept_max_per_connection
-.option "smtp_accept_queue_per_ &~&~connection" main integer 10 &&&
+.option "smtp_accept_queue_per_connection" main integer 10 &&&
smtp_accept_queue_per_connection
.cindex "queueing incoming messages"
.cindex "message" "queueing by message count"
Some of these will be too small to be accepted by clients.
Some may be too large to be accepted by clients.
+.new
+The TLS protocol does not negotiate an acceptable size for this; clients tend
+to hard-drop connections if what is offered by the server is unacceptable,
+whether too large or too small, and there's no provision for the client to
+tell the server what these constraints are. Thus, as a server operator, you
+need to make an educated guess as to what is most likely to work for your
+userbase.
+
+Some known size constraints suggest that a bit-size in the range 2048 to 2236
+is most likely to maximise interoperability. The upper bound comes from
+applications using the Mozilla Network Security Services (NSS) library, which
+used to set its &`DH_MAX_P_BITS`& upper-bound to 2236. This affects many
+mail user agents (MUAs). The lower bound comes from Debian installs of Exim4
+prior to the 4.80 release, as Debian used to patch Exim to raise the minimum
+acceptable bound from 1024 to 2048.
+.wen
+
.option tls_on_connect_ports main "string list" unset
This option specifies a list of incoming SSMTP (aka SMTPS) ports that should
See &<<SECTtlssni>>& for discussion of when this option might be re-expanded.
+.new
+A forced expansion failure or setting to an empty string is equivalent to
+being unset.
+.wen
+
.option tls_verify_hosts main "host list&!!" unset
.cindex "TLS" "client certificate verification"
.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
-option), the string is expanded and included in the debugging output.
+option) or in address-testing mode (see the &%-bt%& command line option),
+the string is expanded and included in the debugging output.
If expansion of the string fails, the error message is written to the debugging
output, and Exim carries on processing.
This option is provided to help with checking out the values of variables and
variables it references. The output happens after checks for &%domains%&,
&%local_parts%&, and &%check_local_user%& but before any other preconditions
are tested. A newline is added to the text if it does not end with one.
+The variable &$router_name$& contains the name of the router.
the expansion is forced to fail, the option has no effect. Other expansion
failures are treated as configuration errors.
+.new
Unlike most options, &%headers_add%& can be specified multiple times
for a router; all listed headers are added.
+.wen
&*Warning 1*&: The &%headers_add%& option cannot be used for a &(redirect)&
router that has the &%one_time%& option set.
.oindex "&%-bv%&"
.cindex "router" "used only when verifying"
If this option is set, the router is used only when verifying an address,
-delivering in cutthrough mode or
+.new "delivering in cutthrough mode or"
testing with the &%-bv%& option, not when actually doing a delivery, testing
with the &%-bt%& option, or running the SMTP EXPN command. It can be further
restricted to verifying only senders or recipients by means of
option is not working properly, &%debug_print%& could be used to output the
variables it references. A newline is added to the text if it does not end with
one.
-
+.new
+The variables &$transport_name$& and &$router_name$& contain the name of the
+transport and the router that called it.
+.wen
.option delivery_date_add transports boolean false
.cindex "&'Delivery-date:'& header line"
is forced to fail, no action is taken. Other expansion failures are treated as
errors and cause the delivery to be deferred.
+.new
Unlike most options, &%headers_add%& can be specified multiple times
for a transport; all listed headers are added.
-
+.wen
.option headers_only transports boolean false
.vindex "&$address_pipe$&"
A router redirects an address directly to a pipe command (for example, from an
alias or forward file). In this case, &$address_pipe$& contains the text of the
-pipe command, and the &%command%& option on the transport is ignored. If only
-one address is being transported (&%batch_max%& is not greater than one, or
-only one address was redirected to this pipe command), &$local_part$& contains
-the local part that was redirected.
+pipe command, and the &%command%& option on the transport is ignored unless
+&%force_command%& is set. If only one address is being transported
+(&%batch_max%& is not greater than one, or only one address was redirected to
+this pipe command), &$local_part$& contains the local part that was redirected.
.endlist
avoids any problems with spaces or shell metacharacters, and is of use when a
&(pipe)& transport is handling groups of addresses in a batch.
+.new
+If &%force_command%& is enabled on the transport, Special handling takes place
+for an argument that consists of precisely the text &`$address_pipe`&. It
+is handled similarly to &$pipe_addresses$& above. It is expanded and each
+argument is inserted in the argument list at that point
+&'as a separate argument'&. The &`$address_pipe`& item does not need to be
+the only item in the argument; in fact, if it were then &%force_command%&
+should behave as a no-op. Rather, it should be used to adjust the command
+run while preserving the argument vector separation.
+.wen
+
After splitting up into arguments and expansion, the resulting command is run
in a subprocess directly from the transport, &'not'& under a shell. The
message that is being delivered is supplied on the standard input, and the
frozen in Exim's queue instead.
+.new
+.option force_command pipe boolean false
+.cindex "force command"
+.cindex "&(pipe)& transport", "force command"
+Normally when a router redirects an address directly to a pipe command
+the &%command%& option on the transport is ignored. If &%force_command%&
+is set, the &%command%& option will used. This is especially
+useful for forcing a wrapper or additional argument to be added to the
+command. For example:
+.code
+command = /usr/bin/remote_exec myhost -- $address_pipe
+force_command
+.endd
+
+Note that &$address_pipe$& is handled specially in &%command%& when
+&%force_command%& is set, expanding out to the original argument vector as
+separate items, similarly to a Unix shell &`"$@"`& construct.
+.wen
+
.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.
are in force when any authenticators are run and when the
&%authenticated_sender%& option is expanded.
+.new
These variables are deprecated in favour of &$tls_in_cipher$& et. al.
and will be removed in a future release.
+.wen
.section "Private options for smtp" "SECID146"
Exim will not try to start a TLS session when delivering to any host that
matches this list. See chapter &<<CHAPTLS>>& for details of TLS.
+.new
.option hosts_verify_avoid_tls smtp "host list&!!" *
.cindex "TLS" "avoiding for certain hosts"
Exim will not try to start a TLS session for a verify callout,
or when delivering in cutthrough mode,
to any host that matches this list.
Note that the default is to not use TLS.
+.wen
.option hosts_max_try smtp integer 5
part.
.cindex "regular expressions" "in retry rules"
-&*Warning*&: If you use a regular expression in a routing rule pattern, it
+&*Warning*&: If you use a regular expression in a retry rule pattern, it
must match a complete address, not just a domain, because that is how regular
expressions work in address lists.
.display
.endd
+.new
.option client_set_id authenticators string&!! unset
When client authentication succeeds, this condition is expanded; the
result is used in the log lines for outbound messasges.
Typically it will be the user name used for authentication.
+.wen
.option driver authenticators string unset
expansion is &"1"&, &"yes"&, or &"true"&, authentication succeeds and the
generic &%server_set_id%& option is expanded and saved in &$authenticated_id$&.
For any other result, a temporary error code is returned, with the expanded
-string as the error text.
+string as the error text
+.new ", and the failed id saved in &$authenticated_fail_id$&."
&*Warning*&: If you use a lookup in the expansion to find the user's
password, be sure to make the authentication fail if the user is unknown.
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),
+&url(http://www.gnutls.org/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)
+&url(http://www.gnutls.org/manual/gnutls.html#Listing-the-ciphersuites-in-a-priority-string, 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
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.
+documentation for &%tls_dhparam%& for the complete list.
See the command
.code
contexts is known as TLS_RSA_WITH_3DES_EDE_CBC_SHA. Check the OpenSSL or GnuTLS
documentation for more details.
+.new
For outgoing SMTP deliveries, &$tls_out_cipher$& is used and logged
(again depending on the &%tls_cipher%& log selector).
+.wen
.section "Requesting and verifying client certificates" "SECID183"
.cindex "certificate" "self-signed"
You can create a self-signed certificate using the &'req'& command provided
with OpenSSL, like this:
+.new
. ==== Do not shorten the duration here without reading and considering
. ==== the text below. Please leave it at 9999 days.
+.wen
.code
openssl req -x509 -newkey rsa:1024 -keyout file1 -out file2 \
-days 9999 -nodes
prompting for the passphrase. This is not helpful if you are going to use
this certificate and key in an MTA, where prompting is not possible.
+.new
. ==== I expect to still be working 26 years from now. The less technical
. ==== debt I create, in terms of storing up trouble for my later years, the
. ==== happier I will be then. We really have reached the point where we
writing, reducing the duration is the most likely choice, but the inexorable
progression of time takes us steadily towards an era where this will not
be a sensible resolution).
+.wen
A self-signed certificate made in this way is sufficient for testing, and
may be adequate for all your requirements if you are mainly interested in
and try again later, but that is their problem, though it does waste some of
your resources.
+.new
The &%acl_smtp_data%& ACL is run after both the &%acl_smtp_dkim%& and
the &%acl_smtp_mime%& ACLs.
-
+.wen
.section "The SMTP DKIM ACL" "SECTDKIMACL"
The &%acl_smtp_dkim%& ACL is available only when Exim is compiled with DKIM support
received, and is executed for each DKIM signature found in a message. If not
otherwise specified, the default action is to accept.
+.new
This ACL is evaluated before &%acl_smtp_mime%& and &%acl_smtp_data%&.
For details on the operation of DKIM, see chapter &<<CHAPdkim>>&.
+.wen
.section "The SMTP MIME ACL" "SECID194"
effect.
+.new
.vitem &*remove_header*&&~=&~<&'text'&>
This modifier specifies one or more header names in a colon-separated list
that are to be removed from an incoming message, assuming, of course, that
the message is ultimately accepted. For details, see section &<<SECTremoveheadacl>>&.
+.wen
.vitem &*set*&&~<&'acl_name'&>&~=&~<&'value'&>
.cindex "&%set%& ACL modifier"
This modifier puts a value into one of the ACL variables (see section
&<<SECTaclvariables>>&).
-.endlist
+.new
+.vitem &*udpsend*&&~=&~<&'parameters'&>
+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
+of a destination server, port number, and the packet contents. The
+server can be specified as a host name or IPv4 or IPv6 address. The
+separator can be changed with the usual angle bracket syntax. For
+example, you might want to collect information on which hosts connect
+when:
+.code
+udpsend = <; 2001:dB8::dead:beef ; 1234 ;\
+ $tod_zulu $sender_host_address
+.endd
+.wen
+.endlist
+
It is usable in the RCPT ACL and valid only for single-recipient mails forwarded
from one SMTP connection to another. If a recipient-verify callout connection is
requested in the same ACL it is held open and used for the data, otherwise one is made
-after the ACL completes. Note that routers are used in verify mode.
+after the ACL completes.
+.new "Note that routers are used in verify mode."
Should the ultimate destination system positively accept or reject the mail,
a corresponding indication is given to the source system and nothing is queued.
.wen
-.new
.vitem &*control&~=&~dkim_disable_verify*&
.cindex "disable DKIM verify"
.cindex "DKIM" "disable verify"
This control turns off DKIM verification processing entirely. For details on
the operation and configuration of DKIM, see chapter &<<CHAPdkim>>&.
-.wen
.new
this, you can use ACL variables, as described in section
&<<SECTaclvariables>>&.
+.new
The list of headers yet to be added is given by the &%$headers_added%& variable.
+.wen
The &%add_header%& modifier acts immediately as it is encountered during the
processing of an ACL. Notice the difference between these two cases:
+.new
.section "Removing header lines in ACLs" "SECTremoveheadacl"
.cindex "header lines" "removing in an ACL"
.cindex "header lines" "position of removed lines"
&*Warning*&: This facility currently applies only to header lines that are
present during ACL processing. It does NOT remove header lines that are added
in a system filter or in a router or transport.
-
+.wen
condition false. This means that further processing of the &%warn%& verb
ceases, but processing of the ACL continues.
+.new
If the argument is a named ACL, up to nine space-separated optional values
can be appended; they appear within the called ACL in $acl_arg1 to $acl_arg9,
and $acl_narg is set to the count of values.
Previous values of these variables are restored after the call returns.
The name and values are expanded separately.
+.wen
If the nested &%acl%& returns &"drop"& and the outer condition denies access,
the connection is dropped. If it returns &"discard"&, the verb must be
LHLO is used instead of HELO if the transport's &%protocol%& option is
set to &"lmtp"&.
+.new
+The callout may use EHLO, AUTH and/or STARTTLS given appropriate option
+settings.
+.wen
+
A recipient callout check is similar. By default, it also uses an empty address
for the sender. This default is chosen because most hosts do not make use of
the sender address when verifying a recipient. Using the same address means
av_scanner = sophie:/var/run/sophie
.endd
If the value of &%av_scanner%& starts with a dollar character, it is expanded
-before use. The following scanner types are supported in this release:
+before use.
+The usual list-parsing of the content (see &<<SECTlistconstruct>>&) applies.
+The following scanner types are supported in this release:
.vlist
.vitem &%aveserver%&
av_scanner = clamd:/opt/clamd/socket
av_scanner = clamd:192.0.2.3 1234
av_scanner = clamd:192.0.2.3 1234:local
+av_scanner = clamd:192.0.2.3 1234 : 192.0.2.4 1234
.endd
If the value of av_scanner points to a UNIX socket file or contains the local
keyword, then the ClamAV interface will pass a filename containing the data
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.
+
+.new
+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
+that only TCP targets may be used if specifying a list of scanners; a UNIX
+socket cannot be mixed in with TCP targets. If one of the servers becomes
+unavailable, Exim will try the remaining one(s) until it finds one that works.
+When a clamd server becomes unreachable, Exim will log a message. Exim does
+not keep track of scanner state between multiple messages, and the scanner
+selection is random, so the message will get logged in the mainlog for each
+email that the down scanner gets chosen first (message wrapped to be readable):
+.code
+2013-10-09 14:30:39 1VTumd-0000Y8-BQ malware acl condition:
+ clamd: connection to localhost, port 3310 failed
+ (Connection refused)
+.endd
+.wen
+
If the option is unset, the default is &_/tmp/clamd_&. Thanks to David Saez for
contributing the code for this scanner.
.endd
Exim does not check the syntax of these added header lines.
+.new
Multiple &%headers_add%& options for a single router or transport can be
specified; the values will be concatenated (with a separating newline
added) before expansion.
+.wen
The result of expanding &%headers_remove%& must consist of a colon-separated
list of header names. This is confusing, because header names themselves are
&`<=`& message arrival
&`=>`& normal message delivery
&`->`& additional address in same delivery
+.new
&`>>`& cutthrough message delivery
+.wen
&`*>`& delivery suppressed by &%-N%&
&`**`& delivery failed; address bounced
&`==`& delivery deferred; temporary problem
last of these is given in parentheses after the final address. The R and T
fields record the router and transport that were used to process the address.
+.new
If SMTP AUTH was used for the delivery there is an additional item A=
followed by the name of the authenticator that was used.
If an authenticated identification was set up by the authenticator's &%client_set_id%&
option, this is logged too, separated by a colon from the authenticator name.
+.wen
If a shadow transport was run after a successful local delivery, the log line
for the successful delivery has an item added on the end, of the form
down a single SMTP connection, an asterisk follows the IP address in the log
lines for the second and subsequent messages.
+.new
.cindex "delivery" "cutthrough; logging"
.cindex "cutthrough" "logging"
When delivery is done in cutthrough mode it is flagged with &`>>`& and the log
line precedes the reception line, since cutthrough waits for a possible
rejection from the destination in case it can reject the sourced item.
+.wen
The generation of a reply message by a filter file gets logged as a
&"delivery"& to the addressee, preceded by &">"&.
The list of optional log items is in the following table, with the default
selection marked by asterisks:
.display
+.new
&` 8bitmime `& received 8BITMIME status
+.wen
&`*acl_warn_skipped `& skipped &%warn%& statement in ACL
&` address_rewrite `& address rewriting
&` all_parents `& all parents in => lines
&`*sender_verify_fail `& sender verification failures
&`*size_reject `& rejection because too big
&`*skip_delivery `& delivery skipped in a queue run
+.new
&`*smtp_confirmation `& SMTP confirmation on => lines
+.wen
&` smtp_connection `& SMTP connections
&` smtp_incomplete_transaction`& incomplete SMTP transactions
+.new
&` smtp_mailauth `& AUTH argument to MAIL commands
+.wen
&` smtp_no_mail `& session with no MAIL commands
&` smtp_protocol_error `& SMTP protocol errors
&` smtp_syntax_error `& SMTP syntax errors
More details on each of these items follows:
.ilist
+.new
.cindex "8BITMIME"
.cindex "log" "8BITMIME"
&%8bitmime%&: This causes Exim to log any 8BITMIME status of received messages,
that are not 8bit clean. This is added to the &"<="& line, tagged with
&`M8S=`& and a value of &`0`&, &`7`& or &`8`&, corresponding to "not given",
&`7BIT`& and &`8BITMIME`& respectively.
+.wen
.next
.cindex "&%warn%& ACL verb" "log when skipping"
&%acl_warn_skipped%&: When an ACL &%warn%& statement is skipped because one of
setting of 10 for &%smtp_accep_max_nonmail%&, the connection will in any case
have been aborted before 20 non-mail commands are processed.
.next
+.new
&%smtp_mailauth%&: A third subfield with the authenticated sender,
colon-separated, is appended to the A= item for a message arrival or delivery
log line, if an AUTH argument to the SMTP MAIL command (see &<<SECTauthparamail>>&)
was accepted or used.
+.wen
.next
.cindex "log" "SMTP protocol error"
.cindex "SMTP" "logging protocol error"
.vlist
.vitem &*-f*&&~<&'regex'&>
-Match the sender address. The field that is tested is enclosed in angle
-brackets, so you can test for bounce messages with
+Match the sender address using a case-insensitive search. The field that is
+tested is enclosed in angle brackets, so you can test for bounce messages with
.code
exiqgrep -f '^<>$'
.endd
.vitem &*-r*&&~<&'regex'&>
-Match a recipient address. The field that is tested is not enclosed in angle
-brackets.
+Match a recipient address using a case-insensitve search. The field that is
+tested is not enclosed in angle brackets.
.vitem &*-s*&&~<&'regex'&>
Match against the size field.
+.new
+.section "Running local commands" "SECTsecconslocalcmds"
+.cindex "security" "local commands"
+.cindex "security" "command injection attacks"
+There are a number of ways in which an administrator can configure Exim to run
+commands based upon received, untrustworthy, data. Further, in some
+configurations a user who can control a &_.forward_& file can also arrange to
+run commands. Configuration to check includes, but is not limited to:
+
+.ilist
+Use of &%use_shell%& in the pipe transport: various forms of shell command
+injection may be possible with this option present. It is dangerous and should
+be used only with considerable caution. Consider constraints which whitelist
+allowed characters in a variable which is to be used in a pipe transport that
+has &%use_shell%& enabled.
+.next
+A number of options such as &%forbid_filter_run%&, &%forbid_filter_perl%&,
+&%forbid_filter_dlfunc%& and so forth which restrict facilities available to
+&_.forward_& files in a redirect router. If Exim is running on a central mail
+hub to which ordinary users do not have shell access, but home directories are
+NFS mounted (for instance) then administrators should review the list of these
+forbid options available, and should bear in mind that the options that may
+need forbidding can change as new features are added between releases.
+.next
+The &%${run...}%& expansion item does not use a shell by default, but
+administrators can configure use of &_/bin/sh_& as part of the command.
+Such invocations should be viewed with prejudicial suspicion.
+.next
+Administrators who use embedded Perl are advised to explore how Perl's
+taint checking might apply to their usage.
+.next
+Use of &%${expand...}%& is somewhat analagous to shell's eval builtin and
+administrators are well advised to view its use with suspicion, in case (for
+instance) it allows a local-part to contain embedded Exim directives.
+.next
+Use of &%${match_local_part...}%& and friends becomes more dangerous if
+Exim was built with EXPAND_LISTMATCH_RHS defined: the second string in
+each can reference arbitrary lists and files, rather than just being a list
+of opaque strings.
+The EXPAND_LISTMATCH_RHS option was added and set false by default because of
+real-world security vulnerabilities caused by its use with untrustworthy data
+injected in, for SQL injection attacks.
+Consider the use of the &%inlisti%& expansion condition instead.
+.endlist
+.wen
+
+
+
+
+.new
+.section "Trust in configuration data" "SECTsecconfdata"
+.cindex "security" "data sources"
+.cindex "security" "regular expressions"
+.cindex "regular expressions" "security"
+.cindex "PCRE" "security"
+If configuration data for Exim can come from untrustworthy sources, there
+are some issues to be aware of:
+
+.ilist
+Use of &%${expand...}%& may provide a path for shell injection attacks.
+.next
+Letting untrusted data provide a regular expression is unwise.
+.next
+Using &%${match...}%& to apply a fixed regular expression against untrusted
+data may result in pathological behaviour within PCRE. Be aware of what
+"backtracking" means and consider options for being more strict with a regular
+expression. Avenues to explore include limiting what can match (avoiding &`.`&
+when &`[a-z0-9]`& or other character class will do), use of atomic grouping and
+possessive quantifiers or just not using regular expressions against untrusted
+data.
+.next
+It can be important to correctly use &%${quote:...}%&,
+&%${quote_local_part:...}%& and &%${quote_%&<&'lookup-type'&>&%:...}%& expansion
+items to ensure that data is correctly constructed.
+.next
+Some lookups might return multiple results, even though normal usage is only
+expected to yield one result.
+.endlist
+.wen
+
+
+
+
.section "IPv4 source routing" "SECID272"
.cindex "source routing" "in IP packets"
.cindex "IP source routing"
A colon-separated list of names of headers included in the signature.
.vitem &%$dkim_key_testing%&
"1" if the key record has the "testing" flag set, "0" if not.
-.vitem &%$nosubdomains%&
+.vitem &%$dkim_key_nosubdomains%&
"1" if the key record forbids subdomaining, "0" otherwise.
.vitem &%$dkim_key_srvtype%&
Service type (tag s=) from the key record. Defaults to "*" if not specified
Edit &_src/drtables.c_&, adding conditional code to pull in the private header
and create a table entry as is done for all the other drivers and lookup types.
.next
+.new
Edit &_scripts/lookups-Makefile_& if this is a new lookup; there is a for-loop
near the bottom, ranging the &`name_mod`& variable over a list of all lookups.
Add your &`NEWDRIVER`& to that list.
As long as the dynamic module would be named &_newdriver.so_&, you can use the
simple form that most lookups have.
+.wen
.next
Edit &_Makefile_& in the appropriate sub-directory (&_src/routers_&,
&_src/transports_&, &_src/auths_&, or &_src/lookups_&); add a line for the new
projects / exim.git / blobdiff