.set I " "
.macro copyyear
-2012
+2014
.endmacro
. /////////////////////////////////////////////////////////////////////////////
<author><firstname>Exim</firstname><surname>Maintainers</surname></author>
<authorinitials>EM</authorinitials>
<revhistory><revision>
- <revnumber>
-.version
- </revnumber>
- <date>
-.fulldate
- </date>
+.versiondatexml
<authorinitials>EM</authorinitials>
</revision></revhistory>
<copyright><year>
.cindex "distribution" "signing details"
.cindex "distribution" "public key"
.cindex "public key for signed distribution"
-.new
The distributions will be PGP signed by an individual key of the Release
Coordinator. This key will have a uid containing an email address in the
&'exim.org'& domain and will have signatures from other people, including
key &'0x403043153903637F'&, although that key is expected to be replaced in 2013.
A trust path from Nigel's key to Phil's can be observed at
&url(https://www.security.spodhuis.org/exim-trustpath).
-.wen
+
+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
&%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.
+Note that cutthrough delivery is classed as a recipient verification for this purpose.
.next
If the &%address_test%& option is set false, the router is skipped when Exim is
run with the &%-bt%& option to test an address routing. This can be helpful
.next
Routers can be designated for use only when verifying an address, as
opposed to routing it for delivery. The &%verify_only%& option controls this.
-Again, cutthrough delibery counts as a verification.
+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).
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%&"
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%&"
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
&`fail`& keyword causes a &'forced expansion failure'& &-- see section
&<<SECTforexpfai>>& for an explanation of what this means.
-The supported DNS record types are A, CNAME, MX, NS, PTR, SPF, SRV, and TXT,
+The supported DNS record types are A, CNAME, MX, NS, PTR, SPF, SRV, TLSA and TXT,
and, when Exim is compiled with IPv6 support, AAAA (and A6 if that is also
configured). If no type is given, TXT is assumed. When the type is PTR,
the data can be an IP address, written as normal; inversion and the addition of
in the same way that multiple DNS records for a single item are handled. A
different separator can be specified, as described above.
+Modifiers for &(dnsdb)& lookups are givien by optional keywords,
+each followed by a comma,
+that may appear before the record type.
+
The &(dnsdb)& lookup fails only if all the DNS lookups fail. If there is a
temporary DNS error for any of them, the behaviour is controlled by
-an optional keyword followed by a comma that may appear before the record
-type. The possible keywords are &"defer_strict"&, &"defer_never"&, and
-&"defer_lax"&. With &"strict"& behaviour, any temporary DNS error causes the
+a defer-option modifier.
+The possible keywords are
+&"defer_strict"&, &"defer_never"&, and &"defer_lax"&.
+With &"strict"& behaviour, any temporary DNS error causes the
whole lookup to defer. With &"never"& behaviour, a temporary DNS error is
ignored, and the behaviour is as if the DNS lookup failed to find anything.
With &"lax"& behaviour, all the queries are attempted, but a temporary DNS
Thus, in the default case, as long as at least one of the DNS lookups
yields some data, the lookup succeeds.
+.new
+.cindex "DNSSEC" "dns lookup"
+Use of &(DNSSEC)& is controlled by a dnssec modifier.
+The possible keywords are
+&"dnssec_strict"&, &"dnssec_lax"&, and &"dnssec_never"&.
+With &"strict"& or &"lax"& DNSSEC information is requested
+with the lookup.
+With &"strict"& a response from the DNS resolver that
+is not labelled as authenticated data
+is treated as equivalent to a temporary DNS error.
+The default is &"never"&.
+
+See also the &$lookup_dnssec_authenticated$& variable.
+.wen
+
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"
&`USER `& set the DN, for authenticating the LDAP bind
&`PASS `& set the password, likewise
&`REFERRALS `& set the referrals parameter
+.new
+&`SERVERS `& set alternate server list for this query only
+.wen
&`SIZE `& set the limit for the number of entries returned
&`TIME `& set the maximum waiting time for a query
.endd
The TIME parameter (also a number of seconds) is passed to the server to
set a server-side limit on the time taken to complete a search.
+.new
+The SERVERS parameter allows you to specify an alternate list of ldap servers
+to use for an individual lookup. The global ldap_servers option provides a
+default list of ldap servers, and a single lookup can specify a single ldap
+server to use. But when you need to do a lookup with a list of servers that is
+different than the default list (maybe different order, maybe a completely
+different set of servers), the SERVERS parameter allows you to specify this
+alternate list.
+.wen
Here is an example of an LDAP query in an Exim lookup that uses some of these
values. This is a single line, folded to fit on the page:
.cindex "&`+include_unknown`&"
.cindex "&`+ignore_unknown`&"
-By default, Exim behaves as if the host does not match the list. This may not
-always be what you want to happen. To change Exim's behaviour, the special
-items &`+include_unknown`& or &`+ignore_unknown`& may appear in the list (at
-top level &-- they are not recognized in an indirected file).
+Exim parses a host list from left to right. If it encounters a permanent
+lookup failure in any item in the host list before it has found a match,
+Exim treats it as a failure and the default behavior is as if the host
+does not match the list. This may not always be what you want to happen.
+To change Exim's behaviour, the special items &`+include_unknown`& or
+&`+ignore_unknown`& may appear in the list (at top level &-- they are
+not recognized in an indirected file).
.ilist
If any item that follows &`+include_unknown`& requires information that
list. The effect of each one lasts until the next, or until the end of the
list.
+.new
+.section "Mixing wildcarded host names and addresses in host lists" &&&
+ "SECTmixwilhos"
+.cindex "host list" "mixing names and addresses in"
+
+This section explains the host/ip processing logic with the same concepts
+as the previous section, but specifically addresses what happens when a
+wildcarded hostname is one of the items in the hostlist.
+
+.ilist
+If you have name lookups or wildcarded host names and
+IP addresses in the same host list, you should normally put the IP
+addresses first. For example, in an ACL you could have:
+.code
+accept hosts = 10.9.8.7 : *.friend.example
+.endd
+The reason you normally would order it this way lies in the
+left-to-right way that Exim processes lists. It can test IP addresses
+without doing any DNS lookups, but when it reaches an item that requires
+a host name, it fails if it cannot find a host name to compare with the
+pattern. If the above list is given in the opposite order, the
+&%accept%& statement fails for a host whose name cannot be found, even
+if its IP address is 10.9.8.7.
+
+.next
+If you really do want to do the name check first, and still recognize the IP
+address, you can rewrite the ACL like this:
+.code
+accept hosts = *.friend.example
+accept hosts = 10.9.8.7
+.endd
+If the first &%accept%& fails, Exim goes on to try the second one. See chapter
+&<<CHAPACL>>& for details of ACLs. Alternatively, you can use
+&`+ignore_unknown`&, which was discussed in depth in the first example in
+this section.
+.endlist
+.wen
+
.section "Temporary DNS errors when looking up host information" &&&
"SECTtemdnserr"
-.section "Mixing wildcarded host names and addresses in host lists" &&&
- "SECTmixwilhos"
-.cindex "host list" "mixing names and addresses in"
-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 for this 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.
-
-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.
-
-
-
.section "Address lists" "SECTaddresslist"
&%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
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.
.cindex "expansion" "case forcing"
.cindex "&%uc%& expansion item"
This forces the letters in the string into upper-case.
+
+.vitem &*${utf8clean:*&<&'string'&>&*}*&
+.cindex "correction of invalid utf-8 sequences in strings"
+.cindex "utf-8" "utf-8 sequences"
+.cindex "incorrect utf-8"
+.cindex "expansion" "utf-8 forcing"
+.cindex "&%utf8clean%& expansion item"
+This replaces any invalid utf-8 sequence in the string by the character &`?`&.
.endlist
.cindex "&%bool%& expansion condition"
This condition turns a string holding a true or false representation into
a boolean state. It parses &"true"&, &"false"&, &"yes"& and &"no"&
-(case-insensitively); also positive integer numbers map to true if non-zero,
+(case-insensitively); also integer numbers map to true if non-zero,
false if zero.
An empty string is treated as false.
Leading and trailing whitespace is ignored;
The value of &$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$&
the space value is -1. See also the &%check_log_space%& option.
+.new
+.vitem &$lookup_dnssec_authenticated$&
+.vindex "&$lookup_dnssec_authenticated$&"
+This variable is set after a DNS lookup done by
+a dnsdb lookup expansion, dnslookup router or smtp transport.
+It will be empty if &(DNSSEC)& was not requested,
+&"no"& if the result was not labelled as authenticated data
+and &"yes"& if it was.
+.wen
+
.vitem &$mailstore_basename$&
.vindex "&$mailstore_basename$&"
This variable is set only when doing deliveries in &"mailstore"& format in the
received. It is empty if there was no successful authentication. See also
&$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$&
.section "TLS" "SECID108"
.table2
.row &%gnutls_compat_mode%& "use GnuTLS compatibility mode"
-.row &%gnutls_enable_pkcs11%& "allow GnuTLS to autoload PKCS11 modules"
+.row &%gnutls_allow_auto_pkcs11%& "allow GnuTLS to autoload PKCS11 modules"
.row &%openssl_options%& "adjust OpenSSL compatibility options"
.row &%tls_advertise_hosts%& "advertise TLS to these hosts"
.row &%tls_certificate%& "location of server certificate"
.row &%disable_ipv6%& "do no IPv6 processing"
.row &%dns_again_means_nonexist%& "for broken domains"
.row &%dns_check_names_pattern%& "pre-DNS syntax check"
+.row &%dns_dnssec_ok%& "parameter for resolver"
.row &%dns_ipv4_lookup%& "only v4 lookup for these domains"
.row &%dns_retrans%& "parameter for resolver"
.row &%dns_retry%& "parameter for resolver"
-.row &%dns_use_dnssec%& "parameter for resolver"
.row &%dns_use_edns0%& "parameter for resolver"
.row &%hold_domains%& "hold delivery for these domains"
.row &%local_interfaces%& "for routing checks"
.code
delay_warning = 2h:12h:99d
.endd
+Note that the option is only evaluated at the time a delivery attempt fails,
+which depends on retry and queue-runner configuration.
+Typically retries will be configured more frequently than warning messages.
.option delay_warning_condition main string&!! "see below"
.vindex "&$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
-.option headers_add routers string&!! unset
+.option headers_add routers list&!! unset
.cindex "header lines" "adding"
.cindex "router" "adding header lines"
-This option specifies a string of text that is expanded at routing time, and
-associated with any addresses that are accepted by the router. However, this
+This option specifies a list of text headers, newline-separated,
+that is associated with any addresses that are accepted by the router.
+Each item is separately expanded, at routing time. However, this
option has no effect when an address is just being verified. The way in which
the text is used to add header lines at transport time is described in section
&<<SECTheadersaddrem>>&. New header lines are not actually added until the
&"see"& the added header lines.
The &%headers_add%& option is expanded after &%errors_to%&, but before
-&%headers_remove%& and &%transport%&. If the expanded string is empty, or if
-the expansion is forced to fail, the option has no effect. Other expansion
+&%headers_remove%& and &%transport%&. If an item is empty, or if
+an item expansion is forced to fail, the item has no effect. Other expansion
failures are treated as configuration errors.
Unlike most options, &%headers_add%& can be specified multiple times
-.option headers_remove routers string&!! unset
+.option headers_remove routers list&!! unset
.cindex "header lines" "removing"
.cindex "router" "removing header lines"
-This option specifies a string of text that is expanded at routing time, and
-associated with any addresses that are accepted by the router. However, this
+This option specifies a list of text headers, colon-separated,
+that is associated with any addresses that are accepted by the router.
+Each item is separately expanded, at routing time. However, this
option has no effect when an address is just being verified. The way in which
the text is used to remove header lines at transport time is described in
section &<<SECTheadersaddrem>>&. Header lines are not actually removed until
&"see"& the original header lines.
The &%headers_remove%& option is expanded after &%errors_to%& and
-&%headers_add%&, but before &%transport%&. If the expansion is forced to fail,
-the option has no effect. Other expansion failures are treated as configuration
+&%headers_add%&, but before &%transport%&. If an item expansion is forced to fail,
+the item has no effect. Other expansion failures are treated as configuration
errors.
Unlike most options, &%headers_remove%& can be specified multiple times
+.new
+.option dnssec_request_domains dnslookup "domain list&!!" unset
+.cindex "MX record" "security"
+.cindex "DNSSEC" "MX lookup"
+.cindex "security" "MX lookup"
+.cindex "DNS" "DNSSEC"
+DNS lookups for domains matching &%dnssec_request_domains%& will be done with
+the dnssec request bit set.
+This applies to all of the SRV, MX A6, AAAA, A lookup sequence.
+.wen
+
+
+
+.new
+.option dnssec_require_domains dnslookup "domain list&!!" unset
+.cindex "MX record" "security"
+.cindex "DNSSEC" "MX lookup"
+.cindex "security" "MX lookup"
+.cindex "DNS" "DNSSEC"
+DNS lookups for domains matching &%dnssec_request_domains%& will be done with
+the dnssec request bit set. Any returns not having the Authenticated Data bit
+(AD bit) set wil be ignored and logged as a host-lookup failure.
+This applies to all of the SRV, MX A6, AAAA, A lookup sequence.
+.wen
+
+
+
.option mx_domains dnslookup "domain list&!!" unset
.cindex "MX record" "required to exist"
.cindex "SRV record" "required to exist"
.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"
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"
If this option is true, a &'Delivery-date:'& header is added to the message.
&%user%& (see below).
-.option headers_add transports string&!! unset
+.option headers_add transports list&!! unset
.cindex "header lines" "adding in transport"
.cindex "transport" "header lines; adding"
-This option specifies a string of text that is expanded and added to the header
+This option specifies a list of text headers, newline-separated,
+which are (separately) expanded and added to the header
portion of a message as it is transported, as described in section
&<<SECTheadersaddrem>>&. Additional header lines can also be specified by
routers. If the result of the expansion is an empty string, or if the expansion
for a transport; all listed headers are added.
-
.option headers_only transports boolean false
.cindex "transport" "header lines only"
.cindex "message" "transporting headers only"
checked, since this option does not automatically suppress them.
-.option headers_remove transports string&!! unset
+.option headers_remove transports list&!! unset
.cindex "header lines" "removing"
.cindex "transport" "header lines; removing"
-This option specifies a string that is expanded into a list of header names;
+This option specifies a list of header names, colon-separated;
these headers are omitted from the message as it is transported, as described
in section &<<SECTheadersaddrem>>&. Header removal can also be specified by
-routers. If the result of the expansion is an empty string, or if the expansion
+routers.
+Each list item is separately expanded.
+If the result of the expansion is an empty string, or if the expansion
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.
+for a router; all listed headers are removed.
.new
+.option dnssec_request_domains smtp "domain list&!!" unset
+.cindex "MX record" "security"
+.cindex "DNSSEC" "MX lookup"
+.cindex "security" "MX lookup"
+.cindex "DNS" "DNSSEC"
+DNS lookups for domains matching &%dnssec_request_domains%& will be done with
+the dnssec request bit set.
+This applies to all of the SRV, MX A6, AAAA, A lookup sequence.
+.wen
+
+
+
+.new
+.option dnssec_require_domains smtp "domain list&!!" unset
+.cindex "MX record" "security"
+.cindex "DNSSEC" "MX lookup"
+.cindex "security" "MX lookup"
+.cindex "DNS" "DNSSEC"
+DNS lookups for domains matching &%dnssec_request_domains%& will be done with
+the dnssec request bit set. Any returns not having the Authenticated Data bit
+(AD bit) set wil be ignored and logged as a host-lookup failure.
+This applies to all of the SRV, MX A6, AAAA, A lookup sequence.
+.wen
+
+
+
.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
in clear.
+.option tls_try_verify_hosts smtp "host list&!! unset
+.cindex "TLS" "server certificate verification"
+.cindex "certificate" "verification of server"
+This option gives a list of hosts for which, on encrypted connections,
+certificate verification will be tried but need not succeed.
+The &%tls_verify_certificates%& option must also be set.
+
+
.option tls_verify_certificates smtp string&!! unset
.cindex "TLS" "server certificate verification"
.cindex "certificate" "verification of server"
&$host_address$& are set to the name and address of the server during the
expansion of this option. See chapter &<<CHAPTLS>>& for details of TLS.
+For back-compatability,
+if neither tls_verify_hosts nor tls_try_verify_hosts are set
+and certificate verification fails the TLS connection is closed.
+
+
+.option tls_verify_hosts smtp "host list&!! unset
+.cindex "TLS" "server certificate verification"
+.cindex "certificate" "verification of server"
+This option gives a list of hosts for which. on encrypted connections,
+certificate verification must succeed.
+The &%tls_verify_certificates%& option must also be set.
+If both this option and &%tls_try_verify_hosts%& are unset
+operation is as if this option selected all hosts.
+
part.
.cindex "regular expressions" "in retry rules"
-&*Warning*&: If you use a regular expression in a routing rule pattern, it
+&*Warning*&: If you use a regular expression in a retry rule pattern, it
must match a complete address, not just a domain, because that is how regular
expressions work in address lists.
.display
expansion is &"1"&, &"yes"&, or &"true"&, authentication succeeds and the
generic &%server_set_id%& option is expanded and saved in &$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
&*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
expected server certificates. The client verifies the server's certificate
against this collection, taking into account any revoked certificates that are
in the list defined by &%tls_crl%&.
+Failure to verify fails the TLS connection unless either of the
+&%tls_verify_hosts%& or &%tls_try_verify_hosts%& options are set.
+
+The &%tls_verify_hosts%& and &%tls_try_verify_hosts%& options restrict
+certificate verification to the listed servers. Verification either must
+or need not succeed respectively.
If
&%tls_require_ciphers%& is set on the &(smtp)& transport, it must contain a
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"
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
enabled (which is the default).
.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 $sender_host_address
+.endd
+.endlist
+
is what is wanted for subsequent tests.
-.new
.vitem &*control&~=&~cutthrough_delivery*&
.cindex "&ACL;" "cutthrough routing"
.cindex "cutthrough" "requesting"
It is usable in the RCPT ACL and valid only for single-recipient mails forwarded
from one SMTP connection to another. If a recipient-verify callout connection is
requested in the same ACL it is held open and used for the data, otherwise one is made
-after the ACL completes. Note that routers are used in verify mode.
+after the ACL completes.
+
+Note that routers are used in verify mode,
+and cannot depend on content of received headers.
+Note also that headers cannot be
+modified by any of the post-data ACLs (DATA, MIME and DKIM).
+Headers may be modified by routers (subject to the above) and transports.
+
+Cutthrough delivery is not supported via transport-filters or when DKIM signing
+of outgoing messages is done, because it sends data to the ultimate destination
+before the entire message has been received from the source.
Should the ultimate destination system positively accept or reject the mail,
a corresponding indication is given to the source system and nothing is queued.
Delivery in this mode avoids the generation of a bounce mail to a (possibly faked)
sender when the destination system is doing content-scan based rejection.
-.wen
-.new
.vitem &*control&~=&~debug/*&<&'options'&>
.cindex "&ACL;" "enabling debug logging"
.cindex "debugging" "enabling from an ACL"
control = debug/opts=+expand+acl
control = debug/tag=.$message_exim_id/opts=+expand
.endd
-.wen
-.new
.vitem &*control&~=&~dkim_disable_verify*&
.cindex "disable DKIM verify"
.cindex "DKIM" "disable verify"
This control turns off DKIM verification processing entirely. For details on
the operation and configuration of DKIM, see chapter &<<CHAPdkim>>&.
-.wen
-.new
.vitem &*control&~=&~dscp/*&<&'value'&>
.cindex "&ACL;" "setting DSCP value"
.cindex "DSCP" "inbound"
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&~=&~enforce_sync*& &&&
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).
+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
remove_header = x-route-mail1 : x-route-mail2
.endd
The &%remove_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
&%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
-
.section "ACL conditions" "SECTaclconditions"
.cindex "&ACL;" "conditions; list of"
Some of the conditions listed in this section are available only when Exim is
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"
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"
&%hosts%& setting, the transport's hosts are used. If an &(smtp)& transport has
&%hosts_override%& set, its hosts are always used, whether or not the router
supplies a host list.
+Callouts are only supported on &(smtp)& transports.
The port that is used is taken from the transport, if it is specified and is a
remote transport. (For routers that do verification only, no transport need be
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.
the transport cannot refer to the modified header lines, because such
expansions all occur before the message is actually transported.
-For both routers and transports, the result of expanding a &%headers_add%&
+For both routers and transports, the argument of a &%headers_add%&
option must be in the form of one or more RFC 2822 header lines, separated by
newlines (coded as &"\n"&). For example:
.code
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.
+specified; the values will append to a single list of header lines.
+Each header-line is separately expanded.
-The result of expanding &%headers_remove%& must consist of a colon-separated
+The argument of a &%headers_remove%& option 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,
not part of the names. For example:
.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.
+specified; the arguments will append to a single header-names list.
+Each item is separately expanded.
-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
+When &%headers_add%& or &%headers_remove%& is specified on a router,
+items are 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
an address passes through several routers as a result of aliasing or
forwarding, the changes are cumulative.
&`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
.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.
.code
exim -bpu
.endd
-to obtain a queue listing with undelivered recipients only, and then greps the
-output to select messages that match given criteria. The following selection
-options are available:
+or (in case &*-a*& switch is specified)
+.code
+exim -bp
+.endd
+.new
+The &*-C*& option is used to specify an alternate &_exim.conf_& which might
+contain alternate exim configuration the queue management might be using.
+.wen
+
+to obtain a queue listing, and then greps the output to select messages
+that match given criteria. The following selection options are available:
.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 '^<>$'
.endd
.vitem &*-r*&&~<&'regex'&>
-Match a recipient address. The field that is tested is not enclosed in angle
-brackets.
+Match a recipient address using a case-insensitve search. The field that is
+tested is not enclosed in angle brackets.
.vitem &*-s*&&~<&'regex'&>
Match against the size field.
.vitem &*-R*&
Display messages in reverse order.
+
+.vitem &*-a*&
+Include delivered recipients in queue listing.
.endlist
There is one more option, &%-h%&, which outputs a list of options.
+.section "Running local commands" "SECTsecconslocalcmds"
+.cindex "security" "local commands"
+.cindex "security" "command injection attacks"
+There are a number of ways in which an administrator can configure Exim to run
+commands based upon received, untrustworthy, data. Further, in some
+configurations a user who can control a &_.forward_& file can also arrange to
+run commands. Configuration to check includes, but is not limited to:
+
+.ilist
+Use of &%use_shell%& in the pipe transport: various forms of shell command
+injection may be possible with this option present. It is dangerous and should
+be used only with considerable caution. Consider constraints which whitelist
+allowed characters in a variable which is to be used in a pipe transport that
+has &%use_shell%& enabled.
+.next
+A number of options such as &%forbid_filter_run%&, &%forbid_filter_perl%&,
+&%forbid_filter_dlfunc%& and so forth which restrict facilities available to
+&_.forward_& files in a redirect router. If Exim is running on a central mail
+hub to which ordinary users do not have shell access, but home directories are
+NFS mounted (for instance) then administrators should review the list of these
+forbid options available, and should bear in mind that the options that may
+need forbidding can change as new features are added between releases.
+.next
+The &%${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 &%${quote_%&<&'lookup-type'&>&%:...}%& expansion
+items to ensure that data is correctly constructed.
+.next
+Some lookups might return multiple results, even though normal usage is only
+expected to yield one result.
+.endlist
+
+
+
+
.section "IPv4 source routing" "SECID272"
.cindex "source routing" "in IP packets"
.cindex "IP source routing"
Exim's DKIM implementation allows to
.olist
Sign outgoing messages: This function is implemented in the SMTP transport.
-It can co-exist with all other Exim features, including transport filters.
+It can co-exist with all other Exim features
+(including transport filters)
+except cutthrough delivery.
.next
Verify signatures in incoming messages: This is implemented by an additional
ACL (acl_smtp_dkim), which can be called several times per message, with
Verification of DKIM signatures in incoming email is implemented via the
&%acl_smtp_dkim%& ACL. By default, this ACL is called once for each
syntactically(!) correct signature in the incoming message.
+A missing ACL definition defaults to accept.
+If any ACL call does not acccept, the message is not accepted.
+If a cutthrough delivery was in progress for the message it is
+summarily dropped (having wasted the transmission effort).
To evaluate the signature in the ACL a large number of expansion variables
containing the signature status and its details are set up during the
A colon-separated list of names of headers included in the signature.
.vitem &%$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
git://git.exim.org / users / heiko / exim.git / blobdiff