.book
. /////////////////////////////////////////////////////////////////////////////
-. These definitions set some parameters and save some typing. Remember that
-. the <bookinfo> element must also be updated for each new edition.
+. These definitions set some parameters and save some typing.
+. Update the Copyright year (only) when changing content.
. /////////////////////////////////////////////////////////////////////////////
.set previousversion "4.80"
-.set version "4.80"
+.include ./local_params
.set ACL "access control lists (ACLs)"
.set I " "
+.macro copyyear
+2014
+.endmacro
. /////////////////////////////////////////////////////////////////////////////
. Additional xfpt markup used by this document, over and above the default
<bookinfo>
<title>Specification of the Exim Mail Transfer Agent</title>
<titleabbrev>The Exim MTA</titleabbrev>
-<date>17 May 2012</date>
+<date>
+.fulldate
+</date>
<author><firstname>Exim</firstname><surname>Maintainers</surname></author>
<authorinitials>EM</authorinitials>
<revhistory><revision>
- <revnumber>4.80</revnumber>
- <date>17 May 2012</date>
+.versiondatexml
<authorinitials>EM</authorinitials>
</revision></revhistory>
-<copyright><year>2012</year><holder>University of Cambridge</holder></copyright>
+<copyright><year>
+.copyyear
+ </year><holder>University of Cambridge</holder></copyright>
</bookinfo>
.literal off
.new
.cindex "documentation"
-This edition of the Exim specification applies to version &version; of Exim.
+This edition of the Exim specification applies to version &version() of Exim.
Substantive changes from the &previousversion; edition are marked in some
renditions of the document; this paragraph is so marked if the rendition is
capable of showing a change indicator.
.cindex "distribution" "signing details"
.cindex "distribution" "public key"
.cindex "public key for signed distribution"
-The distributions are currently signed with Nigel Metheringham's GPG key. The
-corresponding public key is available from a number of keyservers, and there is
-also a copy in the file &_nigel-pubkey.asc_&. The signatures for the tar bundles are
-in:
+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
+other Exim maintainers. We expect that the key will be in the "strong set" of
+PGP keys. There should be a trust path to that key from Nigel Metheringham's
+PGP key, a version of which can be found in the release directory in the file
+&_nigel-pubkey.asc_&. All keys used will be available in public keyserver pools,
+such as &'pool.sks-keyservers.net'&.
+
+At time of last update, releases were being made by Phil Pennock and signed with
+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).
+
+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.
+
+The signatures for the tar bundles are in:
.display
&_exim-n.nn.tar.gz.asc_&
&_exim-n.nn.tar.bz2.asc_&
.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
&%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.
.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 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).
.section "Unpacking" "SECID23"
Exim is distributed as a gzipped or bzipped tar file which, when unpacked,
creates a directory with the name of the current release (for example,
-&_exim-&version;_&) into which the following files are placed:
+&_exim-&version()_&) into which the following files are placed:
.table2 140pt
.irow &_ACKNOWLEDGMENTS_& "contains some acknowledgments"
the subnet 192.168.1.0/24, and from all hosts in &'friendly.domain.example'&.
All other connections are denied. The daemon name used by &'tcpwrappers'&
can be changed at build time by setting TCP_WRAPPERS_DAEMON_NAME in
-in &_Local/Makefile_&, or by setting tcp_wrappers_daemon_name in the
+&_Local/Makefile_&, or by setting tcp_wrappers_daemon_name in the
configure file. Consult the &'tcpwrappers'& documentation for
further details.
For the utility programs, old versions are renamed by adding the suffix &_.O_&
to their names. The Exim binary itself, however, is handled differently. It is
installed under a name that includes the version number and the compile number,
-for example &_exim-&version;-1_&. The script then arranges for a symbolic link
+for example &_exim-&version()-1_&. The script then arranges for a symbolic link
called &_exim_& to point to the binary. If you are updating a previous version
of Exim, the script takes care to ensure that the name &_exim_& is never absent
from the directory (as seen by other processes).
This option is an alias for &%-bV%& and causes version information to be
displayed.
-.new
.vitem &%-Ac%& &&&
&%-Am%&
.oindex "&%-Ac%&"
.oindex "&%-Am%&"
These options are used by Sendmail for selecting configuration files and are
ignored by Exim.
-.wen
.vitem &%-B%&<&'type'&>
.oindex "&%-B%&"
if this is required. If the &%bi_command%& option is not set, calling Exim with
&%-bi%& is a no-op.
-.new
. // Keep :help first, then the rest in alphabetical order
.vitem &%-bI:help%&
.oindex "&%-bI:help%&"
&`SIEVE`& capability response line. As the precise list may depend upon
compile-time build options, which this option will adapt to, this is the only
way to guarantee a correct response.
-.wen
.vitem &%-bm%&
.oindex "&%-bm%&"
.cindex "local message reception"
This option runs an Exim receiving process that accepts an incoming,
-locally-generated message on the current input. The recipients are given as the
+locally-generated message on the standard input. The recipients are given as the
command arguments (except when &%-t%& is also present &-- see below). Each
argument can be a comma-separated list of RFC 2822 addresses. This is the
default option for selecting the overall action of an Exim call; it is assumed
If a list of configuration files was supplied, the value that is output here
is the name of the file that was actually used.
-.new
.cindex "options" "hiding name of"
If the &%-n%& flag is given, then for most modes of &%-bP%& operation the
name will not be output.
-.wen
.cindex "daemon" "process id (pid)"
.cindex "pid (process id)" "of daemon"
.vitem &%-G%&
.oindex "&%-G%&"
.cindex "submission fixups, suppressing (command-line)"
-.new
This option is equivalent to an ACL applying:
.code
control = suppress_local_fixups
As this affects audit information, the caller must be a trusted user to use
this option.
-.wen
.vitem &%-h%&&~<&'number'&>
.oindex "&%-h%&"
no documentation for this option in Solaris 2.4 Sendmail, but the &'mailx'&
command in Solaris 2.4 uses it. See also &%-ti%&.
-.new
.vitem &%-L%&&~<&'tag'&>
.oindex "&%-L%&"
.cindex "syslog" "process name; set with flag"
effect, so early configuration file errors will not honour this flag.
The tag should not be longer than 32 characters.
-.wen
.vitem &%-M%&&~<&'message&~id'&>&~<&'message&~id'&>&~...
.oindex "&%-M%&"
Provided
this error message is successfully sent, the Exim receiving process
exits with a return code of zero. If not, the return code is 2 if the problem
-is that the original message has no recipients, or 1 any other error. This is
-the default &%-oe%&&'x'& option if Exim is called as &'rmail'&.
+is that the original message has no recipients, or 1 for any other error.
+This is the default &%-oe%&&'x'& option if Exim is called as &'rmail'&.
.vitem &%-oem%&
.oindex "&%-oem%&"
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%&
.vitem &%-Tqt%&&~<&'times'&>
.oindex "&%-Tqt%&"
-This an option that is exclusively for use by the Exim testing suite. It is not
+This is an option that is exclusively for use by the Exim testing suite. It is not
recognized when Exim is run normally. It allows for the setting up of explicit
&"queue times"& so that various warning/retry features can be tested.
It sets &%-x%& when calling the MTA from its &%mail%& command. Exim ignores
this option.
-.new
.vitem &%-X%&&~<&'logfile'&>
.oindex "&%-X%&"
This option is interpreted by Sendmail to cause debug information to be sent
to the named file. It is ignored by Exim.
-.wen
.endlist
.ecindex IIDclo1
The authorization code can be &"Y"& for yes, &"N"& for no, &"X"& for explicit
authorization required but absent, or &"?"& for unknown.
+.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
+(see below) is handled separately for each lookup. Example:
+.code
+${lookup dnsdb {>; a+=$sender_helo_name}}
+.endd
+
.section "Multiple dnsdb lookups" "SECID67"
In the previous sections, &(dnsdb)& lookups for a single domain are described.
LDAP connections, rather than the SSL-on-connect &`ldaps`&.
See the &%ldap_start_tls%& option.
+.new
+Starting with Exim 4.83, the initialization of LDAP with TLS is more tightly
+controlled. Every part of the TLS configuration can be configured by settings in
+&_exim.conf_&. Depending on the version of the client libraries installed on
+your system, some of the initialization may have required setting options in
+&_/etc/ldap.conf_& or &_~/.ldaprc_& to get TLS working with self-signed
+certificates. This revealed a nuance where the current UID that exim was
+running as could affect which config files it read. With Exim 4.83, these
+methods become optional, only taking effect if not specifically set in
+&_exim.conf_&.
+.wen
+
.section "LDAP quoting" "SECID68"
.cindex "LDAP" "quoting"
There are several types of pattern that require Exim to know the name of the
remote host. These are either wildcard patterns or lookups by name. (If a
complete hostname is given without any wildcarding, it is used to find an IP
-address to match against, as described in the section &<<SECThoslispatip>>&
+address to match against, as described in section &<<SECThoslispatip>>&
above.)
If the remote host name is not already known when Exim encounters one of these
.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"
operator.
If the query contains a reference to &$sender_host_name$&, Exim automatically
-looks up the host name if has not already done so. (See section
+looks up the host name if it has not already done so. (See section
&<<SECThoslispatnam>>& for comments on finding host names.)
Historical note: prior to release 4.30, Exim would always attempt to find a
surrounding the colons is ignored. For example:
.code
aol.com: spammer1 : spammer2 : ^[0-9]+$ :
-spammer3 : spammer4
+ spammer3 : spammer4
.endd
As in all colon-separated lists in Exim, a colon can be included in an item by
doubling.
Any unused are made empty. The variable &$acl_narg$& is set to the number of
arguments. The named ACL (see chapter &<<CHAPACL>>&) is called
and may use the variables; if another acl expansion is used the values
-are overwritten. If the ACL sets
+are restored after it returns. If the ACL sets
a value using a "message =" modifier and returns accept or deny, the value becomes
the result of the expansion.
-If no message was set and the ACL returned accept or deny
-the value is an empty string.
-If the ACL returned defer the result is a forced-fail. Otherwise the expansion fails.
+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.
.vitem "&*${dlfunc{*&<&'file'&>&*}{*&<&'function'&>&*}{*&<&'arg'&>&*}&&&
&%strlen%&, which gives the length of a string.
+.vitem "&*${listextract{*&<&'number'&>&*}&&&
+ {*&<&'string1'&>&*}{*&<&'string2'&>&*}{*&<&'string3'&>&*}}*&"
+.cindex "expansion" "extracting list elements by number"
+.cindex "&%listextract%&" "extract list elements by number"
+.cindex "list" "extracting elements by number"
+The <&'number'&> argument must consist entirely of decimal digits,
+apart from an optional leading minus,
+and leading and trailing white space (which is ignored).
+
+After expansion, <&'string1'&> is interpreted as a list, colon-separated by
+default, but the separator can be changed in the usual way.
+
+The first field of the list is numbered one.
+If the number is negative, the fields are
+counted from the end of the list, with the rightmost one numbered -1.
+The numbered element of the list is extracted and placed in &$value$&,
+then <&'string2'&> is expanded as the result.
+
+If the modulus of the
+number is zero or greater than the number of fields in the string,
+the result is the expansion of <&'string3'&>.
+
+For example:
+.code
+${listextract{2}{x:42:99}}
+.endd
+yields &"42"&, and
+.code
+${listextract{-3}{<, x,42,99,& Mailer,,/bin/bash}{result: $value}}
+.endd
+yields &"result: 99"&.
+
+If {<&'string3'&>} is omitted, an empty string is used for string3.
+If {<&'string2'&>} is also omitted, the value that was
+extracted is used.
+You can use &`fail`& instead of {<&'string3'&>} as in a string extract.
+
+
.vitem "&*${lookup{*&<&'key'&>&*}&~*&<&'search&~type'&>&*&~&&&
{*&<&'file'&>&*}&~{*&<&'string1'&>&*}&~{*&<&'string2'&>&*}}*&"
This is the first of one of two different types of lookup item, which are both
command does not succeed. If both strings are omitted, the result is contents
of the standard output/error on success, and nothing on failure.
+.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
+troubleshoot:
+.code
+warn condition = ${run{/usr/bin/id}{yes}{no}}
+ log_message = Output of id: $value
+.endd
+If the command requires shell idioms, such as the > redirect operator, the
+shell must be invoked directly, such as with:
+.code
+${run{/bin/bash -c "/usr/bin/id >/tmp/id"}{yes}{yes}}
+.endd
+
.vindex "&$runrc$&"
The return code from the command is put in the variable &$runrc$&, and this
remains set afterwards, so in a filter file you can do things like this:
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 &*${hexquote:*&<&'string'&>&*}*&
+.cindex "quoting" "hex-encoded unprintable characters"
+.cindex "&%hexquote%& expansion item"
+This operator converts non-printable characters in a string into a hex
+escape form. Byte values between 33 (!) and 126 (~) inclusive are left
+as is, and other byte values are converted to &`\xNN`&, for example a
+byte value 127 is converted to &`\x7f`&.
+
+
.vitem &*${lc:*&<&'string'&>&*}*&
.cindex "case forcing in strings"
.cindex "string" "case forcing"
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.
for DNS. For example,
.code
${reverse_ip:192.0.2.4}
-${reverse_ip:2001:0db8:c42:9:1:abcd:192.0.2.3}
+${reverse_ip:2001:0db8:c42:9:1:abcd:192.0.2.127}
.endd
returns
.code
4.2.0.192
-3.0.2.0.0.0.0.c.d.c.b.a.1.0.0.0.9.0.0.0.2.4.c.0.8.b.d.0.1.0.0.2
+f.7.2.0.0.0.0.c.d.c.b.a.1.0.0.0.9.0.0.0.2.4.c.0.8.b.d.0.1.0.0.2
.endd
.cindex "expansion" "case forcing"
.cindex "&%uc%& expansion item"
This forces the letters in the string into upper-case.
+
+.vitem &*${utf8clean:*&<&'string'&>&*}*&
+.cindex "correction of invalid utf-8 sequences in strings"
+.cindex "utf-8" "utf-8 sequences"
+.cindex "incorrect utf-8"
+.cindex "expansion" "utf-8 forcing"
+.cindex "&%utf8clean%& expansion item"
+This replaces any invalid utf-8 sequence in the string by the character &`?`&.
.endlist
Any unused are made empty. The variable &$acl_narg$& is set to the number of
arguments. The named ACL (see chapter &<<CHAPACL>>&) is called
and may use the variables; if another acl expansion is used the values
-are overwritten. If the ACL sets
+are restored after it returns. If the ACL sets
a value using a "message =" modifier the variable $value becomes
the result of the expansion, otherwise it is empty.
If the ACL returns accept the condition is true; if deny, false.
The value of &$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$&
+will contain the failed authentication id. If more than one authentication
+id is attempted, it will contain only the last one. The variable is
+available for processing in the ACL's, generally the quit or notquit ACL.
+A message to a local recipient could still be accepted without requiring
+authentication, which means this variable could also be visible in all of
+the ACL's as well.
.vitem &$authenticated_sender$&
be terminated by colon or white space, because it may contain a wide variety of
characters. Note also that braces must &'not'& be used.
+.vitem &$headers_added$&
+.vindex "&$headers_added$&"
+Within an ACL this variable contains the headers added so far by
+the ACL modifier add_header (section &<<SECTaddheadacl>>&).
+The headers are a newline-separated list.
+
.vitem &$home$&
.vindex "&$home$&"
When the &%check_local_user%& option is set for a router, the user's home
.vindex "&$return_size_limit$&"
This is an obsolete name for &$bounce_return_size_limit$&.
+.vitem &$router_name$&
+.cindex "router" "name"
+.cindex "name" "of router"
+.vindex "&$router_name$&"
+During the running of a router this variable contains its name.
+
.vitem &$runrc$&
.cindex "return code" "from &%run%& expansion"
.vindex "&$runrc$&"
received. It is empty if there was no successful authentication. See also
&$authenticated_id$&.
-.new
.vitem &$sender_host_dnssec$&
.vindex "&$sender_host_dnssec$&"
If &$sender_host_name$& has been populated (by reference, &%hosts_lookup%& or
It is likely that you will need to coerce DNSSEC support on in the resolver
library, by setting:
.code
-dns_use_dnssec = 1
+dns_dnssec_ok = 1
.endd
Exim does not perform DNSSEC validation itself, instead leaving that to a
If you have changed &%host_lookup_order%& so that &`bydns`& is not the first
mechanism in the list, then this variable will be false.
-.wen
.vitem &$sender_host_name$&
This variable contains the UTC date and time in &"Zulu"& format, as specified
by ISO 8601, for example: 20030221154023Z.
+.vitem &$transport_name$&
+.cindex "transport" "name"
+.cindex "name" "of transport"
+.vindex "&$transport_name$&"
+During the running of a transport, this variable contains its name.
+
.vitem &$value$&
.vindex "&$value$&"
This variable contains the result of an expansion lookup, extraction operation,
.endd
To specify listening on the default port on specific interfaces only:
.code
-local_interfaces = 192.168.34.67 : 192.168.34.67
+local_interfaces = 10.0.0.67 : 192.168.34.67
.endd
&*Warning*&: Such a setting excludes listening on the loopback interfaces.
.section "TLS" "SECID108"
.table2
.row &%gnutls_compat_mode%& "use GnuTLS compatibility mode"
-.new
-.row &%gnutls_enable_pkcs11%& "allow GnuTLS to autoload PKCS11 modules"
-.wen
+.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"
.row &%disable_ipv6%& "do no IPv6 processing"
.row &%dns_again_means_nonexist%& "for broken domains"
.row &%dns_check_names_pattern%& "pre-DNS syntax check"
+.row &%dns_dnssec_ok%& "parameter for resolver"
.row &%dns_ipv4_lookup%& "only v4 lookup for these domains"
.row &%dns_retrans%& "parameter for resolver"
.row &%dns_retry%& "parameter for resolver"
-.new
-.row &%dns_use_dnssec%& "parameter for resolver"
-.wen
.row &%dns_use_edns0%& "parameter for resolver"
.row &%hold_domains%& "hold delivery for these domains"
.row &%local_interfaces%& "for routing checks"
.option accept_8bitmime main boolean true
.cindex "8BITMIME"
.cindex "8-bit characters"
+.cindex "log" "selectors"
+.cindex "log" "8BITMIME"
This option causes Exim to send 8BITMIME in its response to an SMTP
EHLO command, and to accept the BODY= parameter on MAIL commands.
However, though Exim is 8-bit clean, it is not a protocol converter, and it
&url(http://cr.yp.to/smtp/8bitmime.html)
.endd
+To log received 8BITMIME status use
+.code
+log_selector = +8bitmime
+.endd
+
.option acl_not_smtp main string&!! unset
.cindex "&ACL;" "for non-SMTP messages"
.cindex "non-SMTP messages" "ACLs for"
.code
delay_warning = 2h:12h:99d
.endd
+Note that the option is only evaluated at the time a delivery attempt fails,
+which depends on retry and queue-runner configuration.
+Typically retries will be configured more frequently than warning messages.
.option delay_warning_condition main string&!! "see below"
.vindex "&$domain$&"
reversed and looked up in the reverse DNS, as described in more detail in
section &<<SECTverifyCSA>>&.
+
+.option dns_dnssec_ok main integer -1
+.cindex "DNS" "resolver options"
+.cindex "DNS" "DNSSEC"
+If this option is set to a non-negative number then Exim will initialise the
+DNS resolver library to either use or not use DNSSEC, overriding the system
+default. A value of 0 coerces DNSSEC off, a value of 1 coerces DNSSEC on.
+
+If the resolver library does not support DNSSEC then this option has no effect.
+
+
.option dns_ipv4_lookup main "domain list&!!" unset
.cindex "IPv6" "DNS lookup for AAAA records"
.cindex "DNS" "IPv6 lookup for AAAA records"
See &%dns_retrans%& above.
-.new
-.option dns_use_dnssec main integer -1
-.cindex "DNS" "resolver options"
-.cindex "DNS" "DNSSEC"
-If this option is set to a non-negative number then Exim will initialise the
-DNS resolver library to either use or not use DNSSEC, overriding the system
-default. A value of 0 coerces DNSSEC off, a value of 1 coerces DNSSEC on.
-
-If the resolver library does not support DNSSEC then this option has no effect.
-.wen
-
-
.option dns_use_edns0 main integer -1
.cindex "DNS" "resolver options"
.cindex "DNS" "EDNS0"
implementations of TLS.
-.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
+&`safari_ecdhe_ecdsa_bug`&
+.next
&`single_dh_use`&
.next
&`single_ecdh_use`&
&`tls_rollback_bug`&
.endlist
+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.
+
.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
See &<<SECTtlssni>>& for discussion of when this option might be re-expanded.
+A forced expansion failure or setting to an empty string is equivalent to
+being unset.
+
.option tls_verify_hosts main "host list&!!" unset
.cindex "TLS" "client certificate verification"
If the result is any other value, the router is run (as this is the last
precondition to be evaluated, all the other preconditions must be true).
-This option is unique in that multiple &%condition%& options may be present.
+This option is unusual in that multiple &%condition%& options may be present.
All &%condition%& options must succeed.
The &%condition%& option provides a means of applying custom conditions to the
.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.
+Unlike most options, &%headers_add%& can be specified multiple times
+for a router; all listed headers are added.
+
&*Warning 1*&: The &%headers_add%& option cannot be used for a &(redirect)&
router that has the &%one_time%& option set.
the option has no effect. Other expansion failures are treated as configuration
errors.
+Unlike most options, &%headers_remove%& can be specified multiple times
+for a router; all listed headers are removed.
+
&*Warning 1*&: The &%headers_remove%& option cannot be used for a &(redirect)&
router that has the &%one_time%& option set.
.cindex "EXPN" "with &%verify_only%&"
.oindex "&%-bv%&"
.cindex "router" "used only when verifying"
-If this option is set, the router is used only when verifying an address or
+If this option is set, the router is used only when verifying an address,
+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 verify_recipient routers&!? boolean true
If this option is false, the router is skipped when verifying recipient
-addresses
+addresses,
+delivering in cutthrough mode
or testing recipient verification using &%-bv%&.
See section &<<SECTrouprecon>>& for a list of the order in which preconditions
are evaluated.
.endd
is interpreted as a pipe with a rather strange command name, and no arguments.
-.new
Note that the above example assumes that the text comes from a lookup source
of some sort, so that the quotes are part of the data. If composing a
redirect router with a &%data%& option directly specifying this command, the
data itself, or avoid using this mechanism and instead create a custom
transport with the &%command%& option set and reference that transport from
an &%accept%& router.
-.wen
.next
.cindex "file" "in redirection list"
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.
-
+The variables &$transport_name$& and &$router_name$& contain the name of the
+transport and the router that called it.
.option delivery_date_add transports boolean false
.cindex "&'Delivery-date:'& header line"
is forced to fail, no action is taken. Other expansion failures are treated as
errors and cause the delivery to be deferred.
+Unlike most options, &%headers_add%& can be specified multiple times
+for a transport; all listed headers are added.
.option headers_only transports boolean false
is forced to fail, no action is taken. Other expansion failures are treated as
errors and cause the delivery to be deferred.
+Unlike most options, &%headers_remove%& can be specified multiple times
+for a router; all listed headers are added.
+
.option headers_rewrite transports string unset
.option transport_filter_timeout transports time 5m
.cindex "transport" "filter, timeout"
-When Exim is reading the output of a transport filter, it a applies a timeout
+When Exim is reading the output of a transport filter, it applies a timeout
that can be set by this option. Exceeding the timeout is normally treated as a
temporary delivery failure. However, if a transport filter is used with a
&(pipe)& transport, a timeout in the transport filter is treated in the same
.vindex "&$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$& contains the local part that was redirected.
.endlist
avoids any problems with spaces or shell metacharacters, and is of use when a
&(pipe)& transport is handling groups of addresses in a batch.
+If &%force_command%& is enabled on the transport, Special handling takes place
+for an argument that consists of precisely the text &`$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.
+
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.
+.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.
+
.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.
details.
-.new
.option dscp smtp string&!! unset
.cindex "DCSP" "outbound"
This option causes the DSCP value associated with a socket to be set to one
that these values will have any effect, not be stripped by networking
equipment, or do much of anything without cooperation with your Network
Engineer and those of all network operators between the source and destination.
-.wen
.option fallback_hosts smtp "string list" unset
be the name of a file that contains a CRL in PEM format.
-.new
.option tls_dh_min_bits smtp integer 1024
.cindex "TLS" "Diffie-Hellman minimum acceptable size"
When establishing a TLS session, if a ciphersuite which uses Diffie-Hellman
will fail.
Only supported when using GnuTLS.
-.wen
.option tls_privatekey smtp string&!! unset
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
+.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.
+
+
.option driver authenticators string unset
This option must always be set. It specifies which of the available
authenticators is to be used.
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
&*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.
The &%tls_require_ciphers%& options operate differently, as described in the
sections &<<SECTreqciphssl>>& and &<<SECTreqciphgnu>>&.
.next
-.new
The &%tls_dh_min_bits%& SMTP transport option is only honoured by GnuTLS.
When using OpenSSL, this option is ignored.
(If an API is found to let OpenSSL be configured in this way,
let the Exim Maintainers know and we'll likely use it).
-.wen
.next
Some other recently added features may only be available in one or the other.
This should be documented with the feature. If the documentation does not
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
root certificate along with the rest makes it available for the user to
install if the receiving end is a client MUA that can interact with a user.
+Note that certificates using MD5 are unlikely to work on today's Internet;
+even if your libraries allow loading them for use in Exim when acting as a
+server, increasingly clients will not accept such certificates. The error
+diagnostics in such a case can be frustratingly vague.
+
+
.section "Self-signed certificates" "SECID187"
.cindex "certificate" "self-signed"
You can create a self-signed certificate using the &'req'& command provided
with OpenSSL, like this:
+. ==== Do not shorten the duration here without reading and considering
+. ==== the text below. Please leave it at 9999 days.
.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.
+. ==== 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
+. ==== should start, at the very least, provoking thought and making folks
+. ==== pause before proceeding, instead of leaving all the fixes until two
+. ==== years before 2^31 seconds after the 1970 Unix epoch.
+. ==== -pdp, 2012
+NB: we are now past the point where 9999 days takes us past the 32-bit Unix
+epoch. If your system uses unsigned time_t (most do) and is 32-bit, then
+the above command might produce a date in the past. Think carefully about
+the lifetime of the systems you're deploying, and either reduce the duration
+of the certificate or reconsider your platform deployment. (At time of
+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).
+
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
encrypting transfers, and not in secure identification.
and try again later, but that is their problem, though it does waste some of
your resources.
+The &%acl_smtp_data%& ACL is run after both the &%acl_smtp_dkim%& and
+the &%acl_smtp_mime%& ACLs.
.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.
-For details on the operation of DKIM, see chapter &<<CHID12>>&.
+This ACL is evaluated before &%acl_smtp_mime%& and &%acl_smtp_data%&.
+
+For details on the operation of DKIM, see chapter &<<CHAPdkim>>&.
.section "The SMTP MIME ACL" "SECID194"
The &%acl_smtp_mime%& option is available only when Exim is compiled with the
content-scanning extension. For details, see chapter &<<CHAPexiscan>>&.
+This ACL is evaluated after &%acl_smtp_dkim%& but before &%acl_smtp_data%&.
+
.section "The QUIT ACL" "SECTQUITACL"
.cindex "QUIT, ACL for"
.section "The not-QUIT ACL" "SECTNOTQUITACL"
.vindex &$acl_smtp_notquit$&
The not-QUIT ACL, specified by &%acl_smtp_notquit%&, is run in most cases when
-an SMTP session ends without sending QUIT. However, when Exim itself is is bad
+an SMTP session ends without sending QUIT. However, when Exim itself is in bad
trouble, such as being unable to write to its log files, this ACL is not run,
because it might try to do things (such as write to log files) that make the
situation even worse.
If &%log_message%& is not present, a &%warn%& verb just checks its conditions
and obeys any &"immediate"& modifiers (such as &%control%&, &%set%&,
-&%logwrite%&, and &%add_header%&) that appear before the first failing
-condition. There is more about adding header lines in section
+&%logwrite%&, &%add_header%&, and &%remove_header%&) that appear before the
+first failing condition. There is more about adding header lines in section
&<<SECTaddheadacl>>&.
If any condition on a &%warn%& statement cannot be completed (that is, there is
warning is generated. The &%control%& modifier affects the way an incoming
message is handled.
-The positioning of the modifiers in an ACL statement important, because the
+The positioning of the modifiers in an ACL statement is important, because the
processing of a verb ceases as soon as its outcome is known. Only those
modifiers that have already been encountered will take effect. For example,
consider this use of the &%message%& modifier:
.vitem &*delay*&&~=&~<&'time'&>
.cindex "&%delay%& ACL modifier"
.oindex "&%-bh%&"
-This modifier may appear in any ACL. It causes Exim to wait for the time
-interval before proceeding. However, when testing Exim using the &%-bh%&
-option, the delay is not actually imposed (an appropriate message is output
-instead). The time is given in the usual Exim notation, and the delay happens
-as soon as the modifier is processed. In an SMTP session, pending output is
-flushed before the delay is imposed.
+This modifier may appear in any ACL except notquit. It causes Exim to wait for
+the time interval before proceeding. However, when testing Exim using the
+&%-bh%& option, the delay is not actually imposed (an appropriate message is
+output instead). The time is given in the usual Exim notation, and the delay
+happens as soon as the modifier is processed. In an SMTP session, pending
+output is flushed before the delay is imposed.
Like &%control%&, &%delay%& can be used with &%accept%& or &%deny%&, for
example:
effect.
+.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>>&.
+
+
.vitem &*set*&&~<&'acl_name'&>&~=&~<&'value'&>
.cindex "&%set%& ACL modifier"
This modifier puts a value into one of the ACL variables (see section
&<<SECTaclvariables>>&).
-.endlist
+.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
+
is what is wanted for subsequent tests.
-.new
.vitem &*control&~=&~cutthrough_delivery*&
.cindex "&ACL;" "cutthrough routing"
+.cindex "cutthrough" "requesting"
This option requests delivery be attempted while the item is being received.
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. Note also that headers cannot be
+modified by any of the post-data ACLs (DATA, MIME and DKIM).
+Cutthrough delivery is not supported via transport-filters or when DKIM signing
+of outgoing messages is done, because it sends data to the ultimate destination
+before the entire message has been received from the source.
+
Should the ultimate destination system positively accept or reject the mail,
a corresponding indication is given to the source system and nothing is queued.
If there is a temporary error the item is queued for later delivery in the
Delivery in this mode avoids the generation of a bounce mail to a (possibly faked)
sender when the destination system is doing content-scan based rejection.
-.wen
-
-
-.new
-.vitem &*control&~=&~dscp/*&<&'value'&>
-.cindex "&ACL;" "setting DSCP value"
-.cindex "DSCP" "inbound"
-This option causes the DSCP value associated with the socket for the inbound
-connection to be adjusted to a given value, given as one of a number of fixed
-strings or to numeric value.
-The &%-bI:dscp%& option may be used to ask Exim which names it knows of.
-Common values include &`throughput`&, &`mincost`&, and on newer systems
-&`ef`&, &`af41`&, etc. Numeric values may be in the range 0 to 0x3F.
-
-The outbound packets from Exim will be marked with this value in the header
-(for IPv4, the TOS field; for IPv6, the TCLASS field); there is no guarantee
-that these values will have any effect, not be stripped by networking
-equipment, or do much of anything without cooperation with your Network
-Engineer and those of all network operators between the source and destination.
-.wen
.vitem &*control&~=&~debug/*&<&'options'&>
.endd
+.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>>&.
+
+
+.vitem &*control&~=&~dscp/*&<&'value'&>
+.cindex "&ACL;" "setting DSCP value"
+.cindex "DSCP" "inbound"
+This option causes the DSCP value associated with the socket for the inbound
+connection to be adjusted to a given value, given as one of a number of fixed
+strings or to numeric value.
+The &%-bI:dscp%& option may be used to ask Exim which names it knows of.
+Common values include &`throughput`&, &`mincost`&, and on newer systems
+&`ef`&, &`af41`&, etc. Numeric values may be in the range 0 to 0x3F.
+
+The outbound packets from Exim will be marked with this value in the header
+(for IPv4, the TOS field; for IPv6, the TCLASS field); there is no guarantee
+that these values will have any effect, not be stripped by networking
+equipment, or do much of anything without cooperation with your Network
+Engineer and those of all network operators between the source and destination.
+
+
.vitem &*control&~=&~enforce_sync*& &&&
&*control&~=&~no_enforce_sync*&
.cindex "SMTP" "synchronization checking"
.section "Adding header lines in ACLs" "SECTaddheadacl"
.cindex "header lines" "adding in an ACL"
.cindex "header lines" "position of added lines"
-.cindex "&%message%& ACL modifier"
+.cindex "&%add_header%& ACL modifier"
The &%add_header%& modifier can be used to add one or more extra header lines
to an incoming message, as in this example:
.code
add_header = X-blacklisted-at: $dnslist_domain
.endd
The &%add_header%& modifier is permitted in the MAIL, RCPT, PREDATA, DATA,
-MIME, and non-SMTP ACLs (in other words, those that are concerned with
+MIME, DKIM, and non-SMTP ACLs (in other words, those that are concerned with
receiving a message). The message must ultimately be accepted for
&%add_header%& to have any significant effect. You can use &%add_header%& with
any ACL verb, including &%deny%& (though this is potentially useful only in a
RCPT ACL).
-If the data for the &%add_header%& modifier contains one or more newlines that
+Headers will not be added to the message if the modifier is used in
+DATA, MIME or DKIM ACLs for messages delivered by cutthrough routing.
+
+Leading and trailing newlines are removed from
+the data for the &%add_header%& modifier; if it then
+contains one or more newlines that
are not followed by a space or a tab, it is assumed to contain multiple header
lines. Each one is checked for valid syntax; &`X-ACL-Warn:`& is added to the
front of any line that is not a valid header line.
are included in the entry that is written to the reject log.
.cindex "header lines" "added; visibility of"
-Header lines are not visible in string expansions until they are added to the
+Header lines are not visible in string expansions
+of message headers
+until they are added to the
message. It follows that header lines defined in the MAIL, RCPT, and predata
ACLs are not visible until the DATA ACL and MIME ACLs are run. Similarly,
header lines that are added by the DATA or MIME ACLs are not visible in those
this, you can use ACL variables, as described in section
&<<SECTaclvariables>>&.
-The &%add_header%& modifier acts immediately it is encountered during the
+The list of headers yet to be added is given by the &%$headers_added%& variable.
+
+The &%add_header%& modifier acts immediately as it is encountered during the
processing of an ACL. Notice the difference between these two cases:
.display
&`accept add_header = ADDED: some text`&
+.section "Removing header lines in ACLs" "SECTremoveheadacl"
+.cindex "header lines" "removing in an ACL"
+.cindex "header lines" "position of removed lines"
+.cindex "&%remove_header%& ACL modifier"
+The &%remove_header%& modifier can be used to remove one or more header lines
+from an incoming message, as in this example:
+.code
+warn message = Remove internal headers
+ remove_header = x-route-mail1 : x-route-mail2
+.endd
+The &%remove_header%& modifier is permitted in the MAIL, RCPT, PREDATA, DATA,
+MIME, DKIM, and non-SMTP ACLs (in other words, those that are concerned with
+receiving a message). The message must ultimately be accepted for
+&%remove_header%& to have any significant effect. You can use &%remove_header%&
+with any ACL verb, including &%deny%&, though this is really not useful for
+any verb that doesn't result in a delivered message.
+
+Headers will not be removed to the message if the modifier is used in
+DATA, MIME or DKIM ACLs for messages delivered by cutthrough routing.
+
+More than one header can be removed at the same time by using a colon separated
+list of header names. The header matching is case insensitive. Wildcards are
+not permitted, nor is list expansion performed, so you cannot use hostlists to
+create a list of headers, however both connection and message variable expansion
+are performed (&%$acl_c_*%& and &%$acl_m_*%&), illustrated in this example:
+.code
+warn hosts = +internal_hosts
+ set acl_c_ihdrs = x-route-mail1 : x-route-mail2
+warn message = Remove internal headers
+ remove_header = $acl_c_ihdrs
+.endd
+Removed header lines are accumulated during the MAIL, RCPT, and predata ACLs.
+They are removed from the message before processing the DATA and MIME ACLs.
+There is no harm in attempting to remove the same header twice nor is removing
+a non-existent header. Further header lines to be removed may be accumulated
+during the DATA and MIME ACLs, after which they are removed from the message,
+if present. In the case of non-SMTP messages, headers to be removed are
+accumulated during the non-SMTP ACLs, and are removed from the message after
+all the ACLs have run. If a message is rejected after DATA or by the non-SMTP
+ACL, there really is no effect because there is no logging of what headers
+would have been removed.
+
+.cindex "header lines" "removed; visibility of"
+Header lines are not visible in string expansions until the DATA phase when it
+is received. Any header lines removed in the MAIL, RCPT, and predata ACLs are
+not visible in the DATA ACL and MIME ACLs. Similarly, header lines that are
+removed by the DATA or MIME ACLs are still visible in those ACLs. Because of
+this restriction, you cannot use header lines as a way of controlling data
+passed between (for example) the MAIL and RCPT ACLs. If you want to do this,
+you should instead use ACL variables, as described in section
+&<<SECTaclvariables>>&.
+
+The &%remove_header%& modifier acts immediately as it is encountered during the
+processing of an ACL. Notice the difference between these two cases:
+.display
+&`accept remove_header = X-Internal`&
+&` `&<&'some condition'&>
+
+&`accept `&<&'some condition'&>
+&` remove_header = X-Internal`&
+.endd
+In the first case, the header line is always removed, whether or not the
+condition is true. In the second case, the header line is removed only if the
+condition is true. Multiple occurrences of &%remove_header%& may occur in the
+same ACL statement. All those that are encountered before a condition fails
+are honoured.
+
+&*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.
+
+
+
.section "ACL conditions" "SECTaclconditions"
.cindex "&ACL;" "conditions; list of"
-Some of conditions listed in this section are available only when Exim is
+Some of the conditions listed in this section are available only when Exim is
compiled with the content-scanning extension. They are included here briefly
for completeness. More detailed descriptions can be found in the discussion on
content scanning in chapter &<<CHAPexiscan>>&.
ceases, but processing of the ACL continues.
If the argument is a named ACL, up to nine space-separated optional values
-can be appended; they appear in $acl_arg1 to $acl_arg9, and $acl_narg is set
-to the count of values. The name and values are expanded separately.
+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.
If the nested &%acl%& returns &"drop"& and the outer condition denies access,
the connection is dropped. If it returns &"discard"&, the verb must be
.endd
-.vitem &*hosts&~=&~*&<&'&~host&~list'&>
+.vitem &*hosts&~=&~*&<&'host&~list'&>
.cindex "&%hosts%& ACL condition"
.cindex "host" "ACL checking"
.cindex "&ACL;" "testing the client host"
send email. Details of how this works are given in section
&<<SECTverifyCSA>>&.
+.new
+.vitem &*verify&~=&~header_names_ascii*&
+.cindex "&%verify%& ACL condition"
+.cindex "&ACL;" "verifying header names only ASCII"
+.cindex "header lines" "verifying header names only ASCII"
+.cindex "verifying" "header names only ASCII"
+This condition is relevant only in an ACL that is run after a message has been
+received, that is, in an ACL specified by &%acl_smtp_data%& or
+&%acl_not_smtp%&. It checks all header names (not the content) to make sure
+there are no non-ASCII characters, also excluding control characters. The
+allowable characters are decimal ASCII values 33 through 126.
+
+Exim itself will handle headers with non-ASCII characters, but it can cause
+problems for downstream applications, so this option will allow their
+detection and rejection in the DATA ACL's.
+.wen
+
.vitem &*verify&~=&~header_sender/*&<&'options'&>
.cindex "&%verify%& ACL condition"
.cindex "&ACL;" "verifying sender in the header"
If the DNS lookup yields both 127.0.0.1 and 127.0.0.2, the condition is
false because 127.0.0.1 matches.
.next
-If &`!==`& or &`!=&&`& is used, the condition is true there is at least one
+If &`!==`& or &`!=&&`& is used, the condition is true if there is at least one
looked up IP address that does not match. Consider:
.code
dnslists = a.b.c!=&0.0.0.1
dnslists = some.list.example
.endd
+If an explicit key is being used for a DNS lookup and it may be an IPv6
+address you should specify alternate list separators for both the outer
+(DNS list name) list and inner (lookup keys) list:
+.code
+ dnslists = <; dnsbl.example.com/<|$acl_m_addrslist
+.endd
+
.section "Rate limiting incoming messages" "SECTratelimiting"
.cindex "rate limiting" "client sending"
.cindex "limiting client sending rates"
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 = 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.
+
+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
+
If the option is unset, the default is &_/tmp/clamd_&. Thanks to David Saez for
contributing the code for this scanner.
.endd
You can safely omit this option (the default value is 1).
+.vitem &%sock%&
+.cindex "virus scanners" "simple socket-connected"
+This is a general-purpose way of talking to simple scanner daemons
+running on the local machine.
+There are four options:
+an address (which may be an IP addres and port, or the path of a Unix socket),
+a commandline to send (may include a single %s which will be replaced with
+the path to the mail file to be scanned),
+an RE to trigger on from the returned data,
+an RE to extract malware_name from the returned data.
+For example:
+.code
+av_scanner = sock:127.0.0.1 6001:%s:(SPAM|VIRUS):(.*)\$
+.endd
+Default for the socket specifier is &_/tmp/malware.sock_&.
+Default for the commandline is &_%s\n_&.
+Both regular-expressions are required.
+
.vitem &%sophie%&
.cindex "virus scanners" "Sophos and Sophie"
Sophie is a daemon that uses Sophos' &%libsavi%& library to scan for viruses.
.endd
Exim does not check the syntax of these added header lines.
+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.
+
The result of expanding &%headers_remove%& must consist of a colon-separated
list of header names. This is confusing, because header names themselves are
often terminated by colons. In this case, the colons are the list separators,
.code
headers_remove = return-receipt-to:acknowledge-to
.endd
+
+Multiple &%headers_remove%& options for a single router or transport can be
+specified; the values will be concatenated (with a separating colon
+added) before expansion.
+
When &%headers_add%& or &%headers_remove%& is specified on a router, its value
is expanded at routing time, and then associated with all addresses that are
accepted by that router, and also with any new addresses that it generates. If
&`<=`& message arrival
&`=>`& normal message delivery
&`->`& additional address in same delivery
+&`>>`& cutthrough message delivery
&`*>`& 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.
+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.
+
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
.display
down a single SMTP connection, an asterisk follows the IP address in the log
lines for the second and subsequent messages.
+.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.
+
The generation of a reply message by a filter file gets logged as a
&"delivery"& to the addressee, preceded by &">"&.
A summary of the field identifiers that are used in log lines is shown in
the following table:
.display
-&`A `& authenticator name (and optional id)
+&`A `& authenticator name (and optional id and sender)
&`C `& SMTP confirmation on delivery
&` `& command list for &"no mail in SMTP session"&
&`CV `& certificate verification status
&`R `& on &`<=`& lines: reference for local bounce
&` `& on &`=>`& &`**`& and &`==`& lines: router name
&`S `& size of message
+&`SNI `& server name indication from TLS client hello
&`ST `& shadow transport name
&`T `& on &`<=`& lines: message subject (topic)
&` `& on &`=>`& &`**`& and &`==`& lines: transport name
The list of optional log items is in the following table, with the default
selection marked by asterisks:
.display
+&` 8bitmime `& received 8BITMIME status
&`*acl_warn_skipped `& skipped &%warn%& statement in ACL
&` address_rewrite `& address rewriting
&` all_parents `& all parents in => lines
&`*smtp_confirmation `& SMTP confirmation on => lines
&` smtp_connection `& SMTP connections
&` smtp_incomplete_transaction`& incomplete SMTP transactions
+&` smtp_mailauth `& AUTH argument to MAIL commands
&` 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
+.cindex "8BITMIME"
+.cindex "log" "8BITMIME"
+&%8bitmime%&: This causes Exim to log any 8BITMIME status of received messages,
+which may help in tracking down interoperability issues with ancient MTAs
+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.
+.next
.cindex "&%warn%& ACL verb" "log when skipping"
&%acl_warn_skipped%&: When an ACL &%warn%& statement is skipped because one of
its conditions cannot be evaluated, a log line to this effect is written if
.next
.cindex "log" "smtp confirmation"
.cindex "SMTP" "logging confirmation"
-&%smtp_confirmation%&: The response to the final &"."& in the SMTP dialogue for
+.cindex "LMTP" "logging confirmation"
+&%smtp_confirmation%&: The response to the final &"."& in the SMTP or LMTP dialogue for
outgoing messages is added to delivery log lines in the form &`C=`&<&'text'&>.
A number of MTAs (including Exim) return an identifying string in this
response.
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
+&%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.
+.next
.cindex "log" "SMTP protocol error"
.cindex "SMTP" "logging protocol error"
&%smtp_protocol_error%&: A log line is written for every SMTP 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 '^<>$'
.endd
.vitem &*-r*&&~<&'regex'&>
-Match a recipient address. The field that is tested is not enclosed in angle
-brackets.
+Match a recipient address using a case-insensitve search. The field that is
+tested is not enclosed in angle brackets.
.vitem &*-s*&&~<&'regex'&>
Match against the size field.
+.section "Running local commands" "SECTsecconslocalcmds"
+.cindex "security" "local commands"
+.cindex "security" "command injection attacks"
+There are a number of ways in which an administrator can configure Exim to run
+commands based upon received, untrustworthy, data. Further, in some
+configurations a user who can control a &_.forward_& file can also arrange to
+run commands. Configuration to check includes, but is not limited to:
+
+.ilist
+Use of &%use_shell%& in the pipe transport: various forms of shell command
+injection may be possible with this option present. It is dangerous and should
+be used only with considerable caution. Consider constraints which whitelist
+allowed characters in a variable which is to be used in a pipe transport that
+has &%use_shell%& enabled.
+.next
+A number of options such as &%forbid_filter_run%&, &%forbid_filter_perl%&,
+&%forbid_filter_dlfunc%& and so forth which restrict facilities available to
+&_.forward_& files in a redirect router. If Exim is running on a central mail
+hub to which ordinary users do not have shell access, but home directories are
+NFS mounted (for instance) then administrators should review the list of these
+forbid options available, and should bear in mind that the options that may
+need forbidding can change as new features are added between releases.
+.next
+The &%${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
+
+
+
+
+.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 &%${quote_%&<&'lookup-type'&>&%:...}%& expansion
+items to ensure that data is correctly constructed.
+.next
+Some lookups might return multiple results, even though normal usage is only
+expected to yield one result.
+.endlist
+
+
+
+
.section "IPv4 source routing" "SECID272"
.cindex "source routing" "in IP packets"
.cindex "IP source routing"
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
-.chapter "Support for DKIM (DomainKeys Identified Mail)" "CHID12" &&&
+.chapter "Support for DKIM (DomainKeys Identified Mail)" "CHAPdkim" &&&
"DKIM Support"
.cindex "DKIM"
Exim's DKIM implementation allows to
.olist
Sign outgoing messages: This function is implemented in the SMTP transport.
-It can co-exist with all other Exim features, including transport filters.
+It can co-exist with all other Exim features
+(including transport filters)
+except cutthrough delivery.
.next
Verify signatures in incoming messages: This is implemented by an additional
ACL (acl_smtp_dkim), which can be called several times per message, with
Verification of DKIM signatures in incoming email is implemented via the
&%acl_smtp_dkim%& ACL. By default, this ACL is called once for each
syntactically(!) correct signature in the incoming message.
+A missing ACL definition defaults to accept.
+If any ACL call does not acccept, the message is not accepted.
+If a cutthrough delivery was in progress for the message it is
+summarily dropped (having wasted the transmission effort).
To evaluate the signature in the ACL a large number of expansion variables
containing the signature status and its details are set up during the
A colon-separated list of names of headers included in the signature.
.vitem &%$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
.vitem &%dkim_status%&
ACL condition that checks a colon-separated list of possible DKIM verification
-results agains the actual result of verification. This is typically used
+results against the actual result of verification. This is typically used
to restrict an ACL verb to a list of verification outcomes, for example:
.code
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
+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.
+.next
Edit &_Makefile_& in the appropriate sub-directory (&_src/routers_&,
&_src/transports_&, &_src/auths_&, or &_src/lookups_&); add a line for the new
driver or lookup type and add it to the definition of OBJ.
git://git.exim.org / users / jgh / exim.git / blobdiff