<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 "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
+.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.
+
.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
.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.
+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
+
+
.section "Temporary DNS errors when looking up host information" &&&
"SECTtemdnserr"
address. See the &*filter*&, &*map*&, and &*reduce*& items for ways of
processing lists.
+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 '${addresses:From: "Last, First" <user@example.com>}'
+user@example.com
+.endd
.vitem &*${base62:*&<&'digits'&>&*}*&
.cindex "&%base62%& expansion item"
be useful for processing the output of the MD5 and SHA-1 hashing functions.
+
+.vitem &*${hexquote:*&<&'string'&>&*}*&
+.cindex "quoting" "hex-encoded unprintable characters"
+.cindex "&%hexquote%& expansion item"
+This operator converts non-printable characters in a string into a hex
+escape form. Byte values between 33 (!) and 126 (~) inclusive are left
+as is, and other byte values are converted to &`\xNN`&, for example a
+byt value 127 is converted to &`\x7f`&.
+
+
.vitem &*${lc:*&<&'string'&>&*}*&
.cindex "case forcing in strings"
.cindex "string" "case forcing"
The value of &$item$& is saved and restored while &*forany*& or &*forall*& is
being processed, to enable these expansion items to be nested.
+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.
+.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.
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
+&`safari_ecdhe_ecdsa_bug`&
+.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.
+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.
+
.option tls_on_connect_ports main "string list" unset
This option specifies a list of incoming SSMTP (aka SMTPS) ports that should
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
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, 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
.cindex "&%set%& ACL modifier"
This modifier puts a value into one of the ACL variables (see section
&<<SECTaclvariables>>&).
+
+
+.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
.endlist
LHLO is used instead of HELO if the transport's &%protocol%& option is
set to &"lmtp"&.
+The callout may use EHLO, AUTH and/or STARTTLS given appropriate option
+settings.
+
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 = 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.
+
+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:
+.code
+2013-10-09 14:30:39 1VTumd-0000Y8-BQ malware acl condition: clamd:\
+ connection to localhost, port 3310 failed (Connection refused)
+.endd
+
If the option is unset, the default is &_/tmp/clamd_&. Thanks to David Saez for
contributing the code for this scanner.
.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.
+.section "Running local commands" "SECTsecconslocalcmds"
+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 &%${match_local_part...}%& and friends becomes more dangerous if
+Exim was built with EXPAND_LISTMATCH_RHS defined: the second string in
+each can reference arbitrary lists and files, rather than just being a list
+of opaque strings.
+The EXPAND_LISTMATCH_RHS option was added and set false by default because of
+real-world security vulnerabilities caused by its use with untrustworthy data
+injected in, for SQL injection attacks.
+Consider the use of the &%inlisti%& expansion condition instead.
+.endlist
+
+
+
.section "IPv4 source routing" "SECID272"
.cindex "source routing" "in IP packets"
.cindex "IP source routing"
A colon-separated list of names of headers included in the signature.
.vitem &%$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
projects / exim.git / blobdiff