. the <bookinfo> element must also be updated for each new edition.
. /////////////////////////////////////////////////////////////////////////////
-.set previousversion "4.75"
+.set previousversion "4.80"
.set version "4.80"
.set ACL "access control lists (ACLs)"
overridden if necessary.
-.new
.section "PCRE library" "SECTpcre"
.cindex "PCRE library"
Exim no longer has an embedded PCRE library as the vast majority of
PCRE support then you will need to obtain and build the current PCRE
from &url(ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/).
More information on PCRE is available at &url(http://www.pcre.org/).
-.wen
.section "DBM libraries" "SECTdb"
.cindex "DBM libraries" "discussion of"
TLS_LIBS=-L/usr/local/openssl/lib -lssl -lcrypto
TLS_INCLUDE=-I/usr/local/openssl/include/
.endd
-.new
.cindex "pkg-config" "OpenSSL"
If you have &'pkg-config'& available, then instead you can just use:
.code
SUPPORT_TLS=yes
USE_OPENSSL_PC=openssl
.endd
-.wen
.cindex "USE_GNUTLS"
If GnuTLS is installed, you should set
.code
TLS_LIBS=-L/usr/gnu/lib -lgnutls -ltasn1 -lgcrypt
TLS_INCLUDE=-I/usr/gnu/include
.endd
-.new
.cindex "pkg-config" "GnuTLS"
If you have &'pkg-config'& available, then instead you can just use:
.code
USE_GNUTLS=yes
USE_GNUTLS_PC=gnutls
.endd
-.wen
You do not need to set TLS_INCLUDE if the relevant directory is already
specified in INCLUDE. Details of how to configure Exim to make use of TLS are
binary, attempts to configure Exim to use it cause run time configuration
errors.
-.new
.cindex "pkg-config" "lookups"
.cindex "pkg-config" "authenticators"
Many systems now use a tool called &'pkg-config'& to encapsulate information
AUTH_HEIMDAL_GSSAPI=yes
AUTH_HEIMDAL_GSSAPI_PC=heimdal-gssapi
.endd
-.wen
.cindex "Perl" "including support for"
Exim can be linked with an embedded Perl interpreter, allowing Perl
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%&"
.cindex "8-bit characters"
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%&"
+.cindex "querying exim information"
+We shall provide various options starting &`-bI:`& for querying Exim for
+information. The output of many of these will be intended for machine
+consumption. This one is not. The &%-bI:help%& option asks Exim for a
+synopsis of supported options beginning &`-bI:`&. Use of any of these
+options shall cause Exim to exit after producing the requested output.
+
+.vitem &%-bI:dscp%&
+.oindex "&%-bI:dscp%&"
+.cindex "DSCP" "values"
+This option causes Exim to emit an alphabetically sorted list of all
+recognised DSCP names.
+
+.vitem &%-bI:sieve%&
+.oindex "&%-bI:sieve%&"
+.cindex "Sieve filter" "capabilities"
+This option causes Exim to emit an alphabetically sorted list of all supported
+Sieve protocol extensions on stdout, one per line. This is anticipated to be
+useful for ManageSieve (RFC 5804) implementations, in providing that protocol's
+&`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"
preference to the address taken from the message. The caller of Exim must be a
trusted user for the sender of a message to be set in this way.
+.vitem &%-bmalware%&&~<&'filename'&>
+.oindex "&%-bmalware%&"
+.cindex "testing", "malware"
+.cindex "malware scan test"
+This debugging option causes Exim to scan the given file,
+using the malware scanning framework. The option of &%av_scanner%& influences
+this option, so if &%av_scanner%&'s value is dependent upon an expansion then
+the expansion should have defaults which apply to this invocation. ACLs are
+not invoked, so if &%av_scanner%& references an ACL variable then that variable
+will never be populated and &%-bmalware%& will fail.
+
+Exim will have changed working directory before resolving the filename, so
+using fully qualified pathnames is advisable. Exim will be running as the Exim
+user when it tries to open the file, rather than as the invoking user.
+This option requires admin privileges.
+
+The &%-bmalware%& option will not be extended to be more generally useful,
+there are better tools for file-scanning. This option exists to help
+administrators verify their Exim and AV scanner configuration.
+
.vitem &%-bnq%&
.oindex "&%-bnq%&"
.cindex "address qualification, suppressing"
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"
If &%log_file_path%& or &%pid_file_path%& are given, the names of the
Exim behaves in exactly the same way as it does when receiving a message via
the listening daemon.
-.vitem &%-bmalware%&&~<&'filename'&>
-.oindex "&%-bmalware%&"
-.cindex "testing", "malware"
-.cindex "malware scan test"
-This debugging option causes Exim to scan the given file,
-using the malware scanning framework. The option of &%av_scanner%& influences
-this option, so if &%av_scanner%&'s value is dependent upon an expansion then
-the expansion should have defaults which apply to this invocation. ACLs are
-not invoked, so if &%av_scanner%& references an ACL variable then that variable
-will never be populated and &%-bmalware%& will fail.
-
-Exim will have changed working directory before resolving the filename, so
-using fully qualified pathnames is advisable. Exim will be running as the Exim
-user when it tries to open the file, rather than as the invoking user.
-This option requires admin privileges.
-
-The &%-bmalware%& option will not be extended to be more generally useful,
-there are better tools for file-scanning. This option exists to help
-administrators verify their Exim and AV scanner configuration.
-
.vitem &%-bt%&
.oindex "&%-bt%&"
.cindex "testing" "addresses"
.vitem &%-G%&
.oindex "&%-G%&"
-.cindex "Sendmail compatibility" "&%-G%& option ignored"
-This is a Sendmail option which is ignored by Exim.
+.cindex "submission fixups, suppressing (command-line)"
+.new
+This option is equivalent to an ACL applying:
+.code
+control = suppress_local_fixups
+.endd
+for every message received. Note that Sendmail will complain about such
+bad formatting, where Exim silently just does not fix it up. This may change
+in future.
+
+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"
+This option is equivalent to setting &%syslog_processname%& in the config
+file and setting &%log_file_path%& to &`syslog`&.
+Its use is restricted to administrators. The configuration file has to be
+read and parsed, to determine access rights, before this is set and takes
+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%&"
.cindex "forcing delivery"
.vitem &%-n%&
.oindex "&%-n%&"
-.cindex "Sendmail compatibility" "&%-n%& option ignored"
-This option is interpreted by Sendmail to mean &"no aliasing"&. It is ignored
-by Exim.
+This option is interpreted by Sendmail to mean &"no aliasing"&.
+For normal modes of operation, it is ignored by Exim.
+When combined with &%-bP%& it suppresses the name of an option from being output.
.vitem &%-O%&&~<&'data'&>
.oindex "&%-O%&"
National Language Support extended characters in the body of the mail item"&).
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 first three non-comment configuration lines are as follows:
.code
-domainlist local_domains = @
+domainlist local_domains = @
domainlist relay_to_domains =
hostlist relay_from_hosts = 127.0.0.1
.endd
fact authenticate until you complete the authenticator definitions.
.code
require message = relay not permitted
- domains = +local_domains : +relay_domains
+ domains = +local_domains : +relay_to_domains
.endd
This statement rejects the address if its domain is neither a local domain nor
one of the domains for which this host is a relay.
# server_set_id = $auth2
# server_prompts = :
# server_condition = Authentication is not yet configured
-# server_advertise_condition = ${if def:tls_cipher }
+# server_advertise_condition = ${if def:tls_in_cipher }
.endd
And the example LOGIN authenticator looks like this:
.code
# server_set_id = $auth1
# server_prompts = <| Username: | Password:
# server_condition = Authentication is not yet configured
-# server_advertise_condition = ${if def:tls_cipher }
+# server_advertise_condition = ${if def:tls_in_cipher }
.endd
The &%server_set_id%& option makes Exim remember the authenticated username
i.e. PLAIN or LOGIN. The &%server_advertise_condition%& setting controls
when Exim offers authentication to clients; in the examples, this is only
when TLS or SSL has been started, so to enable the authenticators you also
-need to add support for TLS as described in &<<SECTdefconfmain>>&.
+need to add support for TLS as described in section &<<SECTdefconfmain>>&.
The &%server_condition%& setting defines how to verify that the username and
password are correct. In the examples it just produces an error message.
To make the authenticators work, you can use a string expansion
-expression like one of the examples in &<<CHAPplaintext>>&.
+expression like one of the examples in chapter &<<CHAPplaintext>>&.
Beware that the sequence of the parameters to PLAIN and LOGIN differ; the
-usercode and password are in different positions. &<<CHAPplaintext>>&
-covers both.
+usercode and password are in different positions.
+Chapter &<<CHAPplaintext>>& covers both.
.ecindex IIDconfiwal
the DB_UNKNOWN option. This enables it to handle any of the types of database
that the library supports, and can be useful for accessing DBM files created by
other applications. (For earlier DB versions, DB_HASH is always used.)
-.new
.next
.cindex "lookup" "dbmjz"
.cindex "lookup" "dbm &-- embedded NULs"
authenticate incoming SMTP calls using the passwords from Cyrus SASL's
&_/etc/sasldb2_& file with the &(gsasl)& authenticator or Exim's own
&(cram_md5)& authenticator.
-.wen
.next
.cindex "lookup" "dbmnz"
.cindex "lookup" "dbm &-- terminating zero"
&`fail`& keyword causes a &'forced expansion failure'& &-- see section
&<<SECTforexpfai>>& for an explanation of what this means.
-.new
The supported DNS record types are A, CNAME, MX, NS, PTR, SPF, SRV, 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-addr.arpa%& or &%ip6.arpa%& happens automatically. For example:
-.wen
.code
${lookup dnsdb{ptr=192.168.4.5}{$value}fail}
.endd
.cindex "TXT record" "in &(dnsdb)& lookup"
.cindex "SPF record" "in &(dnsdb)& lookup"
-.new
For TXT records with multiple items of data, only the first item is returned,
unless a separator for them is specified using a comma after the separator
character followed immediately by the TXT record item separator. To concatenate
items without a separator, use a semicolon instead. For SPF records the
default behaviour is to concatenate multiple items without using a separator.
-.wen
.code
${lookup dnsdb{>\n,: txt=a.b.example}}
${lookup dnsdb{>\n; txt=a.b.example}}
.endd
In a list, the syntax is similar. For example:
.code
-domainlist relay_domains = sqlite;/some/thing/sqlitedb \
+domainlist relay_to_domains = sqlite;/some/thing/sqlitedb \
select * from relays where ip='$sender_host_address';
.endd
The only character affected by the &%quote_sqlite%& operator is a single
subject having matched any of the patterns, it is in the set if the last item
was a negative one, but not if it was a positive one. For example, the list in
.code
-domainlist relay_domains = !a.b.c : *.b.c
+domainlist relay_to_domains = !a.b.c : *.b.c
.endd
matches any domain ending in &'.b.c'& except for &'a.b.c'&. Domains that match
neither &'a.b.c'& nor &'*.b.c'& do not match, because the last item in the
list is positive. However, if the setting were
.code
-domainlist relay_domains = !a.b.c
+domainlist relay_to_domains = !a.b.c
.endd
then all domains other than &'a.b.c'& would match because the last item in the
list is negative. In other words, a list that ends with a negative item behaves
respectively. Then there follows the name that you are defining, followed by an
equals sign and the list itself. For example:
.code
-hostlist relay_hosts = 192.168.23.0/24 : my.friend.example
+hostlist relay_from_hosts = 192.168.23.0/24 : my.friend.example
addresslist bad_senders = cdb;/etc/badsenders
.endd
A named list may refer to other named lists:
supplied number and is at least 0. The quality of this randomness depends
on how Exim was built; the values are not suitable for keying material.
If Exim is linked against OpenSSL then RAND_pseudo_bytes() is used.
-.new
If Exim is linked against GnuTLS then gnutls_rnd(GNUTLS_RND_NONCE) is used,
for versions of GnuTLS with that function.
-.wen
Otherwise, the implementation may be arc4random(), random() seeded by
srandomdev() or srandom(), or a custom implementation even weaker than
random().
.endd
Note that the general negation operator provides for inequality testing. The
two strings must take the form of optionally signed decimal integers,
-optionally followed by one of the letters &"K"& or &"M"& (in either upper or
-lower case), signifying multiplication by 1024 or 1024*1024, respectively.
+optionally followed by one of the letters &"K"&, &"M"& or &"G"& (in either upper or
+lower case), signifying multiplication by 1024, 1024*1024 or 1024*1024*1024, respectively.
As a special case, the numerical value of an empty string is taken as
zero.
includes the case of letters, whereas for &%gti%& the comparison is
case-independent.
-.new
.vitem &*inlist&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& &&&
&*inlisti&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*&
.cindex "string" "comparison"
${if inlisti{Needle}{fOo:NeeDLE:bAr}}
${if forany{fOo:NeeDLE:bAr}{eqi{$item}{Needle}}}
.endd
-.wen
.vitem &*isip&~{*&<&'string'&>&*}*& &&&
&*isip4&~{*&<&'string'&>&*}*& &&&
.vitem &*match_ip&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*&
.cindex "&%match_ip%& expansion condition"
-.new
This condition matches an IP address to a list of IP address patterns. It must
be followed by two argument strings. The first (after expansion) must be an IP
address or an empty string. The second (not expanded) is a restricted host
list that can match only an IP address, not a host name. For example:
-.wen
.code
${if match_ip{$sender_host_address}{1.2.3.4:5.6.7.8}{...}{...}}
.endd
.endd
.endlist ilist
-.new
Note that <&'string2'&> is not itself subject to string expansion, unless
Exim was built with the EXPAND_LISTMATCH_RHS option.
-.wen
Consult section &<<SECThoslispatip>>& for further details of these patterns.
have their local parts matched casefully. Domains are always matched
caselessly.
-.new
Note that <&'string2'&> is not itself subject to string expansion, unless
Exim was built with the EXPAND_LISTMATCH_RHS option.
-.wen
&*Note*&: Host lists are &'not'& supported in this way. This is because
hosts have two identities: a name and an IP address, and it is not clear
negative response to an AUTH command, including (for example) an attempt to use
an undefined mechanism.
-.new
.vitem &$av_failed$&
.cindex "content scanning" "AV scanner failure"
This variable is available when Exim is compiled with the content-scanning
extension. It is set to &"0"& by default, but will be set to &"1"& if any
problem occurs with the virus scanner (specified by &%av_scanner%&) during
the ACL malware condition.
-.wen
.vitem &$body_linecount$&
.cindex "message body" "line count"
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
+otherwise) then this boolean will have been set true if, and only if, the
+resolver library states that the reverse DNS was authenticated data. At all
+other times, this variable is false.
+
+It is likely that you will need to coerce DNSSEC support on in the resolver
+library, by setting:
+.code
+dns_use_dnssec = 1
+.endd
+
+Exim does not perform DNSSEC validation itself, instead leaving that to a
+validating resolver (eg, unbound, or bind with suitable configuration).
+
+Exim does not (currently) check to see if the forward DNS was also secured
+with DNSSEC, only the reverse DNS.
+
+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 &$sender_host_name$&
.vindex "&$sender_host_name$&"
When a message is received from a remote host, this variable contains the
command, which can be found in the separate document entitled &'Exim's
interfaces to mail filtering'&.
-.new
-.vitem &$tls_bits$&
-.vindex "&$tls_bits$&"
-Contains an approximation of the TLS cipher's bit-strength; the meaning of
+.vitem &$tls_in_bits$&
+.vindex "&$tls_in_bits$&"
+Contains an approximation of the TLS cipher's bit-strength
+on the inbound connection; the meaning of
this depends upon the TLS implementation used.
If TLS has not been negotiated, the value will be 0.
The value of this is automatically fed into the Cyrus SASL authenticator
when acting as a server, to specify the "external SSF" (a SASL term).
-.wen
-.vitem &$tls_certificate_verified$&
-.vindex "&$tls_certificate_verified$&"
+The deprecated &$tls_bits$& variable refers to the inbound side
+except when used in the context of an outbound SMTP delivery, when it refers to
+the outbound.
+
+.vitem &$tls_out_bits$&
+.vindex "&$tls_out_bits$&"
+Contains an approximation of the TLS cipher's bit-strength
+on an outbound SMTP connection; the meaning of
+this depends upon the TLS implementation used.
+If TLS has not been negotiated, the value will be 0.
+
+.vitem &$tls_in_certificate_verified$&
+.vindex "&$tls_in_certificate_verified$&"
This variable is set to &"1"& if a TLS certificate was verified when the
message was received, and &"0"& otherwise.
-.vitem &$tls_cipher$&
+The deprecated &$tls_certificate_verfied$& variable refers to the inbound side
+except when used in the context of an outbound SMTP delivery, when it refers to
+the outbound.
+
+.vitem &$tls_out_certificate_verified$&
+.vindex "&$tls_out_certificate_verified$&"
+This variable is set to &"1"& if a TLS certificate was verified when an
+outbound SMTP connection was made,
+and &"0"& otherwise.
+
+.vitem &$tls_in_cipher$&
+.vindex "&$tls_in_cipher$&"
.vindex "&$tls_cipher$&"
When a message is received from a remote host over an encrypted SMTP
connection, this variable is set to the cipher suite that was negotiated, for
&$tls_cipher$& for emptiness is one way of distinguishing between encrypted and
non-encrypted connections during ACL processing.
-The &$tls_cipher$& variable retains its value during message delivery, except
-when an outward SMTP delivery takes place via the &(smtp)& transport. In this
-case, &$tls_cipher$& is cleared before any outgoing SMTP connection is made,
+The deprecated &$tls_cipher$& variable is the same as &$tls_in_cipher$& during message reception,
+but in the context of an outward SMTP delivery taking place via the &(smtp)& transport
+becomes the same as &$tls_out_cipher$&.
+
+.vitem &$tls_out_cipher$&
+.vindex "&$tls_out_cipher$&"
+This variable is
+cleared before any outgoing SMTP connection is made,
and then set to the outgoing cipher suite if one is negotiated. See chapter
&<<CHAPTLS>>& for details of TLS support and chapter &<<CHAPsmtptrans>>& for
details of the &(smtp)& transport.
-.vitem &$tls_peerdn$&
+.vitem &$tls_in_peerdn$&
+.vindex "&$tls_in_peerdn$&"
.vindex "&$tls_peerdn$&"
When a message is received from a remote host over an encrypted SMTP
connection, and Exim is configured to request a certificate from the client,
the value of the Distinguished Name of the certificate is made available in the
-&$tls_peerdn$& during subsequent processing. Like &$tls_cipher$&, the
-value is retained during message delivery, except during outbound SMTP
-deliveries.
+&$tls_in_peerdn$& during subsequent processing.
-.new
-.vitem &$tls_sni$&
+The deprecated &$tls_peerdn$& variable refers to the inbound side
+except when used in the context of an outbound SMTP delivery, when it refers to
+the outbound.
+
+.vitem &$tls_out_peerdn$&
+.vindex "&$tls_out_peerdn$&"
+When a message is being delivered to a remote host over an encrypted SMTP
+connection, and Exim is configured to request a certificate from the server,
+the value of the Distinguished Name of the certificate is made available in the
+&$tls_out_peerdn$& during subsequent processing.
+
+.vitem &$tls_in_sni$&
+.vindex "&$tls_in_sni$&"
.vindex "&$tls_sni$&"
.cindex "TLS" "Server Name Indication"
When a TLS session is being established, if the client sends the Server
a different certificate to be presented (and optionally a different key to be
used) to the client, based upon the value of the SNI extension.
-The value will be retained for the lifetime of the message. During outbound
-SMTP deliveries, it reflects the value of the &%tls_sni%& option on
+The deprecated &$tls_sni$& variable refers to the inbound side
+except when used in the context of an outbound SMTP delivery, when it refers to
+the outbound.
+
+.vitem &$tls_out_sni$&
+.vindex "&$tls_out_sni$&"
+.cindex "TLS" "Server Name Indication"
+During outbound
+SMTP deliveries, this variable reflects the value of the &%tls_sni%& option on
the transport.
-.wen
.vitem &$tod_bsdinbox$&
.vindex "&$tod_bsdinbox$&"
.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"
Those options that undergo string expansion before use are marked with
†.
-.new
.option accept_8bitmime main boolean true
.cindex "8BITMIME"
.cindex "8-bit characters"
.display
&url(http://cr.yp.to/smtp/8bitmime.html)
.endd
-.wen
.option acl_not_smtp main string&!! unset
.cindex "&ACL;" "for non-SMTP messages"
is encrypted using TLS, you can make use of the fact that the value of this
option is expanded, with a setting like this:
.code
-auth_advertise_hosts = ${if eq{$tls_cipher}{}{}{*}}
+auth_advertise_hosts = ${if eq{$tls_in_cipher}{}{}{*}}
.endd
-.vindex "&$tls_cipher$&"
-If &$tls_cipher$& is empty, the session is not encrypted, and the result of
+.vindex "&$tls_in_cipher$&"
+If &$tls_in_cipher$& is empty, the session is not encrypted, and the result of
the expansion is empty, thus matching no hosts. Otherwise, the result of the
expansion is *, which matches all hosts.
.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"
on.
If the resolver library does not support EDNS0 then this option has no effect.
-.wen
.option drop_cr main boolean false
transport driver.
-.option openssl_options main "string list" unset
+.option openssl_options main "string list" "+no_sslv2"
.cindex "OpenSSL "compatibility options"
This option allows an administrator to adjust the SSL options applied
by OpenSSL to connections. It is given as a space-separated list of items,
adjusted lightly. An unrecognised item will be detected at startup, by
invoking Exim with the &%-bV%& flag.
-.new
Historical note: prior to release 4.80, Exim defaulted this value to
"+dont_insert_empty_fragments", which may still be needed for compatibility
with some clients, but which lowers security by increasing exposure to
some now infamous attacks.
-.wen
An example:
.code
${if def:sender_helo_name {(helo=$sender_helo_name)\n\t}}}}\
by $primary_hostname \
${if def:received_protocol {with $received_protocol}} \
- ${if def:tls_cipher {($tls_cipher)\n\t}}\
+ ${if def:tls_in_cipher {($tls_in_cipher)\n\t}}\
(Exim $version_number)\n\t\
${if def:sender_address \
{(envelope-from <$sender_address>)\n\t}}\
. Allow this long option name to split; give it unsplit as a fifth argument
. for the automatic .oindex that is generated by .option.
-.option "smtp_accept_max_per_ &~&~connection" main integer 1000 &&&
+.option "smtp_accept_max_per_connection" main integer 1000 &&&
smtp_accept_max_per_connection
.cindex "SMTP" "limiting incoming message count"
.cindex "limit" "messages per SMTP connection"
use when sending messages as a client, you must set the &%tls_certificate%&
option in the relevant &(smtp)& transport.
-.new
-If the option contains &$tls_sni$& and Exim is built against OpenSSL, then
+If the option contains &$tls_out_sni$& and Exim is built against OpenSSL, then
if the OpenSSL build supports TLS extensions and the TLS client sends the
Server Name Indication extension, then this option and others documented in
&<<SECTtlssni>>& will be re-expanded.
-.wen
.option tls_crl main string&!! unset
.cindex "TLS" "server certificate revocation list"
This option specifies a certificate revocation list. The expanded value must
be the name of a file that contains a CRL in PEM format.
-.new
See &<<SECTtlssni>>& for discussion of when this option might be re-expanded.
-.wen
-.new
.option tls_dh_max_bits main integer 2236
.cindex "TLS" "D-H bit count"
The number of bits used for Diffie-Hellman key-exchange may be suggested by
If you prefer more security and are willing to break some clients, raise this
number.
-.wen
+
+Note that the value passed to GnuTLS for *generating* a new prime may be a
+little less than this figure, because GnuTLS is inexact and may produce a
+larger prime than requested.
.option tls_dhparam main string&!! unset
.cindex "TLS" "D-H parameters for server"
-The value of this option is expanded, and must then be the absolute path to
-a file which contains the server's DH parameter values.
-This is used only for OpenSSL. When Exim is linked with GnuTLS, this option is
-ignored. See section &<<SECTopenvsgnu>>& for further details.
+The value of this option is expanded and indicates the source of DH parameters
+to be used by Exim.
-.new
-If the DH bit-count from loading the file is greater than tls_dh_max_bits then
-it will be ignored.
-.end
+If it is a filename starting with a &`/`&, then it names a file from which DH
+parameters should be loaded. If the file exists, it should hold a PEM-encoded
+PKCS#3 representation of the DH prime. If the file does not exist, for
+OpenSSL it is an error. For GnuTLS, Exim will attempt to create the file and
+fill it with a generated DH prime. For OpenSSL, if the DH bit-count from
+loading the file is greater than &%tls_dh_max_bits%& then it will be ignored,
+and treated as though the &%tls_dhparam%& were set to "none".
+
+If this option expands to the string "none", then no DH parameters will be
+loaded by Exim.
+
+If this option expands to the string "historic" and Exim is using GnuTLS, then
+Exim will attempt to load a file from inside the spool directory. If the file
+does not exist, Exim will attempt to create it.
+See section &<<SECTgnutlsparam>>& for further details.
+
+If Exim is using OpenSSL and this option is empty or unset, then Exim will load
+a default DH prime; the default is the 2048 bit prime described in section
+2.2 of RFC 5114, "2048-bit MODP Group with 224-bit Prime Order Subgroup", which
+in IKE is assigned number 23.
+
+Otherwise, the option must expand to the name used by Exim for any of a number
+of DH primes specified in RFC 2409, RFC 3526 and RFC 5114. As names, Exim uses
+"ike" followed by the number used by IKE, of "default" which corresponds to
+"ike23".
+
+The available primes are:
+&`ike1`&, &`ike2`&, &`ike5`&,
+&`ike14`&, &`ike15`&, &`ike16`&, &`ike17`&, &`ike18`&,
+&`ike22`&, &`ike23`& (aka &`default`&) and &`ike24`&.
+
+Some of these will be too small to be accepted by clients.
+Some may be too large to be accepted by clients.
.option tls_on_connect_ports main "string list" unset
key is assumed to be in the same file as the server's certificates. See chapter
&<<CHAPTLS>>& for further details.
-.new
See &<<SECTtlssni>>& for discussion of when this option might be re-expanded.
-.wen
.option tls_remember_esmtp main boolean false
Thus the values defined should be considered public data. To avoid this,
use OpenSSL with a directory.
-.new
See &<<SECTtlssni>>& for discussion of when this option might be re-expanded.
-.wen
.option tls_verify_hosts main "host list&!!" unset
case routing fails.
+.section "Declining addresses by dnslookup" "SECTdnslookupdecline"
+.cindex "&(dnslookup)& router" "declines"
+There are a few cases where a &(dnslookup)& router will decline to accept
+an address; if such a router is expected to handle "all remaining non-local
+domains", then it is important to set &%no_more%&.
+
+Reasons for a &(dnslookup)& router to decline currently include:
+.ilist
+The domain does not exist in DNS
+.next
+The domain exists but the MX record's host part is just "."; this is a common
+convention (borrowed from SRV) used to indicate that there is no such service
+for this domain and to not fall back to trying A/AAAA records.
+.next
+Ditto, but for SRV records, when &%check_srv%& is set on this router.
+.next
+MX record points to a non-existent host.
+.next
+MX record points to an IP address and the main section option
+&%allow_mx_to_ip%& is not set.
+.next
+MX records exist and point to valid hosts, but all hosts resolve only to
+addresses blocked by the &%ignore_target_hosts%& generic option on this router.
+.next
+The domain is not syntactically valid (see also &%allow_utf8_domains%& and
+&%dns_check_names_pattern%& for handling one variant of this)
+.next
+&%check_secondary_mx%& is set on this router but the local host can
+not be found in the MX records (see below)
+.endlist
+
+
.section "Private options for dnslookup" "SECID118"
.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
+quotes will be used by the configuration parser to define the extent of one
+string, but will not be passed down into the redirect router itself. There
+are two main approaches to get around this: escape quotes to be part of 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"
.cindex "address redirection" "to file"
section &<<SECTmaildirdelivery>>& below.
-.new
.option maildir_use_size_file appendfile&!! boolean false
.cindex "maildir format" "&_maildirsize_& file"
The result of string expansion for this option must be a valid boolean value.
quota from the &%quota%& option of the transport. If &%quota%& is unset, the
value is zero. See &%maildir_quota_directory_regex%& above and section
&<<SECTmaildirdelivery>>& below for further details.
-.wen
.option maildirfolder_create_regex appendfile string unset
.cindex "maildir format" "&_maildirfolder_& file"
are in force when any authenticators are run and when the
&%authenticated_sender%& option is expanded.
+These variables are deprecated in favour of &$tls_in_cipher$& et. al.
+and will be removed in a future release.
+
.section "Private options for smtp" "SECID146"
.cindex "options" "&(smtp)& transport"
The expansion happens after the outgoing connection has been made and TLS
started, if required. This means that the &$host$&, &$host_address$&,
-&$tls_cipher$&, and &$tls_peerdn$& variables are set according to the
+&$tls_out_cipher$&, and &$tls_out_peerdn$& variables are set according to the
particular connection.
If the SMTP session is not authenticated, the expansion of
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
+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
+
.option fallback_hosts smtp "string list" unset
.cindex "fallback" "hosts specified on transport"
Exim will not try to start a TLS session when delivering to any host that
matches this list. See chapter &<<CHAPTLS>>& for details of TLS.
+.option hosts_verify_avoid_tls smtp "host list&!!" *
+.cindex "TLS" "avoiding for certain hosts"
+Exim will not try to start a TLS session for a verify callout,
+or when delivering in cutthrough mode,
+to any host that matches this list.
+Note that the default is to not use TLS.
+
.option hosts_max_try smtp integer 5
.cindex "host" "maximum number to try"
deliveries into closed message stores. Exim also has support for running LMTP
over a pipe to a local process &-- see chapter &<<CHAPLMTP>>&.
-.new
If this option is set to &"smtps"&, the default vaule for the &%port%& option
changes to &"smtps"&, and the transport initiates TLS immediately after
connecting, as an outbound SSL-on-connect, instead of using STARTTLS to upgrade.
The Internet standards bodies strongly discourage use of this mode.
-.wen
.option retry_include_ip_address smtp boolean true
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
+key agreement is negotiated, the server will provide a large prime number
+for use. This option establishes the minimum acceptable size of that number.
+If the parameter offered by the server is too small, then the TLS handshake
+will fail.
+
+Only supported when using GnuTLS.
+.wen
+
+
.option tls_privatekey smtp string&!! unset
.cindex "TLS" "client private key, location of"
.vindex "&$host$&"
-.new
.option tls_sni smtp string&!! unset
.cindex "TLS" "Server Name Indication"
.vindex "&$tls_sni$&"
-If this option is set then it sets the $tls_sni variable and causes any
+If this option is set then it sets the $tls_out_sni variable and causes any
TLS session to pass this value as the Server Name Indication extension to
the remote side, which can be used by the remote side to select an appropriate
certificate and private key for the session.
See &<<SECTtlssni>>& for more information.
-OpenSSL only, also requiring a build of OpenSSL that supports TLS extensions.
-.wen
+Note that for OpenSSL, this feature requires a build of OpenSSL that supports
+TLS extensions.
+
.code
AUTH_CRAM_MD5=yes
AUTH_CYRUS_SASL=yes
-.new
AUTH_DOVECOT=yes
AUTH_GSASL=yes
AUTH_HEIMDAL_GSSAPI=yes
-.wen
AUTH_PLAINTEXT=yes
AUTH_SPA=yes
.endd
in &_Local/Makefile_&, respectively. The first of these supports the CRAM-MD5
authentication mechanism (RFC 2195), and the second provides an interface to
the Cyrus SASL authentication library.
-.new
The third is an interface to Dovecot's authentication system, delegating the
work via a socket interface.
The fourth provides an interface to the GNU SASL authentication library, which
the PLAIN authentication mechanism (RFC 2595) or the LOGIN mechanism, which is
not formally documented, but used by several MUAs. The seventh authenticator
supports Microsoft's &'Secure Password Authentication'& mechanism.
-.wen
The authenticators are configured using the same syntax as other drivers (see
section &<<SECTfordricon>>&). If no authenticators are required, no
authenticators, followed by general discussion of the way authentication works
in Exim.
-.new
&*Beware:*& the meaning of &$auth1$&, &$auth2$&, ... varies on a per-driver and
per-mechanism basis. Please read carefully to determine which variables hold
account labels such as usercodes and which hold passwords or other
to a client to help it select an account and credentials to use. In some
mechanisms, the client and server provably agree on the realm, but clients
typically can not treat the realm as secure data to be blindly trusted.
-.wen
used, for example, to skip plain text authenticators when the connection is not
encrypted by a setting such as:
.code
-client_condition = ${if !eq{$tls_cipher}{}}
+client_condition = ${if !eq{$tls_out_cipher}{}}
.endd
-(Older documentation incorrectly states that &$tls_cipher$& contains the cipher
-used for incoming messages. In fact, during SMTP delivery, it contains the
-cipher used for the delivery.)
.option driver authenticators string unset
is used directly to control authentication. See section &<<SECTplainserver>>&
for details.
-.new
For the &(gsasl)& authenticator, this option is required for various
mechanisms; see chapter &<<CHAPgsasl>>& for details.
-.wen
For the other authenticators, &%server_condition%& can be used as an additional
authentication or authorization mechanism that is applied after the other
advertisement of a particular mechanism to encrypted connections, by a setting
such as:
.code
-server_advertise_condition = ${if eq{$tls_cipher}{}{no}{yes}}
+server_advertise_condition = ${if eq{$tls_in_cipher}{}{no}{yes}}
.endd
-.vindex "&$tls_cipher$&"
-If the session is encrypted, &$tls_cipher$& is not empty, and so the expansion
+.vindex "&$tls_in_cipher$&"
+If the session is encrypted, &$tls_in_cipher$& is not empty, and so the expansion
yields &"yes"&, which allows the advertisement to happen.
When an Exim server receives an AUTH command from a client, it rejects it
Note that this expansion explicitly forces failure if the lookup fails
because &$auth1$& contains an unknown user name.
-.new
As another example, if you wish to re-use a Cyrus SASL sasldb2 file without
using the relevant libraries, you need to know the realm to specify in the
lookup and then ask for the &"userPassword"& attribute for that user in that
dbmjz{/etc/sasldb2}}
server_set_id = $auth1
.endd
-.wen
.section "Using cram_md5 as a client" "SECID177"
.cindex "options" "&(cram_md5)& authenticator (client)"
changing the server keytab might need to be communicated down to the Kerberos
layer independently. The mechanism for doing so is dependent upon the Kerberos
implementation.
-.new
+
For example, for older releases of Heimdal, the environment variable KRB5_KTNAME
may be set to point to an alternative keytab file. Exim will pass this
variable through from its own inherited environment when started as root or the
environment variable. In practice, for those releases, the Cyrus authenticator
is not a suitable interface for GSSAPI (Kerberos) support. Instead, consider
the &(heimdal_gssapi)& authenticator, described in chapter &<<CHAPheimdalgss>>&
-.wen
.section "Using cyrus_sasl as a server" "SECID178"
server_set_id = $auth1
.endd
-.new
.option server_realm cyrus_sasl string&!! unset
This specifies the SASL realm that the server claims to be in.
-.wen
.option server_service cyrus_sasl string &`smtp`&
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
-.new
.chapter "The gsasl authenticator" "CHAPgsasl"
.scindex IIDgsaslauth1 "&(gsasl)& authenticator"
.scindex IIDgsaslauth2 "authenticators" "&(gsasl)&"
server_condition = yes
.endd
-.wen
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
-.new
.chapter "The heimdal_gssapi authenticator" "CHAPheimdalgss"
.scindex IIDheimdalgssauth1 "&(heimdal_gssapi)& authenticator"
.scindex IIDheimdalgssauth2 "authenticators" "&(heimdal_gssapi)&"
GSS Display Name.
.endlist
-.wen
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
The &%tls_verify_certificates%& option must contain the name of a file, not the
name of a directory (for OpenSSL it can be either).
.next
-The &%tls_dhparam%& option is ignored, because early versions of GnuTLS had no
-facility for varying its Diffie-Hellman parameters. I understand that this has
-changed, but Exim has not been updated to provide this facility.
-.new
-Instead, the GnuTLS support will use a file from the spool directory.
-.wen
+The default value for &%tls_dhparam%& differs for historical reasons.
.next
-.vindex "&$tls_peerdn$&"
+.vindex "&$tls_in_peerdn$&"
+.vindex "&$tls_out_peerdn$&"
Distinguished Name (DN) strings reported by the OpenSSL library use a slash for
separating fields; GnuTLS uses commas, in accordance with RFC 2253. This
-affects the value of the &$tls_peerdn$& variable.
+affects the value of the &$tls_in_peerdn$& and &$tls_out_peerdn$& variables.
.next
OpenSSL identifies cipher suites using hyphens as separators, for example:
-DES-CBC3-SHA. GnuTLS uses underscores, for example: RSA_ARCFOUR_SHA. What is
-more, OpenSSL complains if underscores are present in a cipher list. To make
-life simpler, Exim changes underscores to hyphens for OpenSSL and hyphens to
-underscores for GnuTLS when processing lists of cipher suites in the
+DES-CBC3-SHA. GnuTLS historically used underscores, for example:
+RSA_ARCFOUR_SHA. What is more, OpenSSL complains if underscores are present
+in a cipher list. To make life simpler, Exim changes underscores to hyphens
+for OpenSSL and passes the string unchanged to GnuTLS (expecting the library
+to handle its own older variants) when processing lists of cipher suites in the
&%tls_require_ciphers%& options (the global option and the &(smtp)& transport
option).
.next
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
explicitly state that the feature is infeasible in the other TLS
implementation, then patches are welcome.
-.wen
.endlist
-.section "GnuTLS parameter computation" "SECID181"
-.new
+.section "GnuTLS parameter computation" "SECTgnutlsparam"
+This section only applies if &%tls_dhparam%& is set to &`historic`& or to
+an explicit path; if the latter, then the text about generation still applies,
+but not the chosen filename.
+By default, as of Exim 4.80 a hard-coded D-H prime is used.
+See the documentation of &%tls_dhparam%& for more information.
+
GnuTLS uses D-H parameters that may take a substantial amount of time
to compute. It is unreasonable to re-compute them for every TLS session.
Therefore, Exim keeps this data in a file in its spool directory, called
For maximum security, the parameters that are stored in this file should be
recalculated periodically, the frequency depending on your paranoia level.
+If you are avoiding using the fixed D-H primes published in RFCs, then you
+are concerned about some advanced attacks and will wish to do this; if you do
+not regenerate then you might as well stick to the standard primes.
+
Arranging this is easy in principle; just delete the file when you want new
values to be computed. However, there may be a problem. The calculation of new
parameters needs random numbers, and these are obtained from &_/dev/random_&.
renaming. The relevant commands are something like this:
.code
# ls
-[ look for file; assume gnutls-params-1024 is the most recent ]
+[ look for file; assume gnutls-params-2236 is the most recent ]
# rm -f new-params
# touch new-params
# chown exim:exim new-params
# chmod 0600 new-params
-# certtool --generate-dh-params --bits 1024 >>new-params
+# certtool --generate-dh-params --bits 2236 >>new-params
+# openssl dhparam -noout -text -in new-params | head
+[ check the first line, make sure it's not more than 2236;
+ if it is, then go back to the start ("rm") and repeat
+ until the size generated is at most the size requested ]
# chmod 0400 new-params
-# mv new-params gnutls-params-1024
+# mv new-params gnutls-params-2236
.endd
If Exim never has to generate the parameters itself, the possibility of
stalling is removed.
Exim will choose depends upon the version of GnuTLS in use. For older GnuTLS,
the value remains hard-coded in Exim as 1024. As of GnuTLS 2.12.x, there is
a way for Exim to ask for the "normal" number of bits for D-H public-key usage,
-and Exim does so. Exim thus removes itself from the policy decision, and the
-filename and bits used change as the GnuTLS maintainers change the value for
-their parameter &`GNUTLS_SEC_PARAM_NORMAL`&. At the time of writing, this
-gives 2432 bits.
-.wen
+and Exim does so. This attempt to remove Exim from TLS policy decisions
+failed, as GnuTLS 2.12 returns a value higher than the current hard-coded limit
+of the NSS library. Thus Exim gains the &%tls_dh_max_bits%& global option,
+which applies to all D-H usage, client or server. If the value returned by
+GnuTLS is greater than &%tls_dh_max_bits%& then the value will be clamped down
+to &%tls_dh_max_bits%&. The default value has been set at the current NSS
+limit, which is still much higher than Exim historically used.
+
+The filename and bits used will change as the GnuTLS maintainers change the
+value for their parameter &`GNUTLS_SEC_PARAM_NORMAL`&, as clamped by
+&%tls_dh_max_bits%&. At the time of writing (mid 2012), GnuTLS 2.12 recommends
+2432 bits, while NSS is limited to 2236 bits.
+
+In fact, the requested value will be *lower* than &%tls_dh_max_bits%&, to
+increase the chance of the generated prime actually being within acceptable
+bounds, as GnuTLS has been observed to overshoot. Note the check step in the
+procedure above. There is no sane procedure available to Exim to double-check
+the size of the generated prime, so it might still be too large.
.section "Requiring specific ciphers in OpenSSL" "SECTreqciphssl"
suites before the cipher negotiation takes place. This specifies which ciphers
are acceptable. The list is colon separated and may contain names like
DES-CBC3-SHA. Exim passes the expanded value of &%tls_require_ciphers%&
-directly to this function call. The following quotation from the OpenSSL
+directly to this function call.
+Many systems will install the OpenSSL manual-pages, so you may have
+&'ciphers(1)'& available to you.
+The following quotation from the OpenSSL
documentation specifies what forms of item are allowed in the cipher string:
.ilist
not be moved to the end of the list.
.endlist
+The OpenSSL &'ciphers(1)'& command may be used to test the results of a given
+string:
+.code
+# note single-quotes to get ! past any shell history expansion
+$ openssl ciphers 'HIGH:!MD5:!SHA1'
+.endd
+
+This example will let the library defaults be permitted on the MX port, where
+there's probably no identity verification anyway, but ups the ante on the
+submission ports where the administrator might have some influence on the
+choice of clients used:
+.code
+# OpenSSL variant; see man ciphers(1)
+tls_require_ciphers = ${if =={$received_port}{25}\
+ {DEFAULT}\
+ {HIGH:!MD5:!SHA1}}
+.endd
+
-.new
.section "Requiring specific ciphers or other parameters in GnuTLS" &&&
"SECTreqciphgnu"
.cindex "GnuTLS" "specifying parameters for"
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.gnu.org/software/gnutls/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)
+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
additional options, "&%gnutls_require_kx%&", "&%gnutls_require_mac%&" and
"&%gnutls_require_protocols%&". &%tls_require_ciphers%& was an Exim list.
-.wen
+
+This example will let the library defaults be permitted on the MX port, where
+there's probably no identity verification anyway, and lowers security further
+by increasing compatibility; but this ups the ante on the submission ports
+where the administrator might have some influence on the choice of clients
+used:
+.code
+# GnuTLS variant
+tls_require_ciphers = ${if =={$received_port}{25}\
+ {NORMAL:%COMPAT}\
+ {SECURE128}}
+.endd
.section "Configuring an Exim server to use TLS" "SECID182"
tls_dhparam = /some/file/name
.endd
is set, the SSL library is initialized for the use of Diffie-Hellman ciphers
-with the parameters contained in the file. This increases the set of cipher
-suites that the server supports. See the command
+with the parameters contained in the file.
+Set this to &`none`& to disable use of DH entirely, by making no prime
+available:
+.code
+tls_dhparam = none
+.endd
+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.
+
+See the command
.code
openssl dhparam
.endd
-for a way of generating this data. At present, &%tls_dhparam%& is used only
-when Exim is linked with OpenSSL. It is ignored if GnuTLS is being used.
+for a way of generating file data.
The strings supplied for these three options are expanded every time a client
host connects. It is therefore possible to use different certificates and keys
.cindex "cipher" "logging"
.cindex "log" "TLS cipher"
-.vindex "&$tls_cipher$&"
-The variable &$tls_cipher$& is set to the cipher suite that was negotiated for
+.vindex "&$tls_in_cipher$&"
+The variable &$tls_in_cipher$& is set to the cipher suite that was negotiated for
an incoming TLS connection. It is included in the &'Received:'& header of an
incoming message (by default &-- you can, of course, change this), and it is
also included in the log line that records a message's arrival, keyed by
&"X="&, unless the &%tls_cipher%& log selector is turned off. The &%encrypted%&
condition can be used to test for specific cipher suites in ACLs.
-(For outgoing SMTP deliveries, &$tls_cipher$& is reset &-- see section
-&<<SECID185>>&.)
Once TLS has been established, the ACLs that run for subsequent SMTP commands
can check the name of the cipher suite and vary their actions accordingly. The
contexts is known as TLS_RSA_WITH_3DES_EDE_CBC_SHA. Check the OpenSSL or GnuTLS
documentation for more details.
+For outgoing SMTP deliveries, &$tls_out_cipher$& is used and logged
+(again depending on the &%tls_cipher%& log selector).
+
.section "Requesting and verifying client certificates" "SECID183"
.cindex "certificate" "verification of client"
example, you can insist on a certificate before accepting a message for
relaying, but not when the message is destined for local delivery.
-.vindex "&$tls_peerdn$&"
+.vindex "&$tls_in_peerdn$&"
When a client supplies a certificate (whether it verifies or not), the value of
the Distinguished Name of the certificate is made available in the variable
-&$tls_peerdn$& during subsequent processing of the message.
+&$tls_in_peerdn$& during subsequent processing of the message.
.cindex "log" "distinguished name"
Because it is often a long text string, it is not included in the log line or
&'Received:'& header by default. You can arrange for it to be logged, keyed by
&"DN="&, by setting the &%tls_peerdn%& log selector, and you can use
&%received_header_text%& to change the &'Received:'& header. When no
-certificate is supplied, &$tls_peerdn$& is empty.
+certificate is supplied, &$tls_in_peerdn$& is empty.
.section "Revoked certificates" "SECID184"
which the client is connected. Forced failure of an expansion causes Exim to
behave as if the relevant option were unset.
-.vindex &$tls_bits$&
-.vindex &$tls_cipher$&
-.vindex &$tls_peerdn$&
-.vindex &$tls_sni$&
+.vindex &$tls_out_bits$&
+.vindex &$tls_out_cipher$&
+.vindex &$tls_out_peerdn$&
+.vindex &$tls_out_sni$&
Before an SMTP connection is established, the
-&$tls_bits$&, &$tls_cipher$&, &$tls_peerdn$& and &$tls_sni$&
+&$tls_out_bits$&, &$tls_out_cipher$&, &$tls_out_peerdn$& and &$tls_out_sni$&
variables are emptied. (Until the first connection, they contain the values
that were set when the message was received.) If STARTTLS is subsequently
successfully obeyed, these variables are set to the relevant values for the
-.new
.section "Use of TLS Server Name Indication" "SECTtlssni"
.cindex "TLS" "Server Name Indication"
-.vindex "&$tls_sni$&"
-.oindex "&%tls_sni%&"
+.vindex "&$tls_in_sni$&"
+.oindex "&%tls_in_sni%&"
With TLS1.0 or above, there is an extension mechanism by which extra
information can be included at various points in the protocol. One of these
extensions, documented in RFC 6066 (and before that RFC 4366) is
The &%tls_sni%& option on an SMTP transport is an expanded string; the result,
if not empty, will be sent on a TLS session as part of the handshake. There's
nothing more to it. Choosing a sensible value not derived insecurely is the
-only point of caution. The &$tls_sni$& variable will be set to this string
+only point of caution. The &$tls_out_sni$& variable will be set to this string
for the lifetime of the client connection (including during authentication).
-Except during SMTP client sessions, if &$tls_sni$& is set then it is a string
+Except during SMTP client sessions, if &$tls_in_sni$& is set then it is a string
received from a client.
It can be logged with the &%log_selector%& item &`+tls_sni`&.
-If the string &`tls_sni`& appears in the main section's &%tls_certificate%&
+If the string &`tls_in_sni`& appears in the main section's &%tls_certificate%&
option (prior to expansion) then the following options will be re-expanded
during TLS session handshake, to permit alternative values to be chosen:
When Exim is built against GnuTLS, SNI support is available as of GnuTLS
0.5.10. (Its presence predates the current API which Exim uses, so if Exim
built, then you have SNI support).
-.wen
This modifier sets up a message that is used as part of the log message if the
ACL denies access or a &%warn%& statement's conditions are true. For example:
.code
-require log_message = wrong cipher suite $tls_cipher
+require log_message = wrong cipher suite $tls_in_cipher
encrypted = DES-CBC3-SHA
.endd
&%log_message%& is also used when recipients are discarded by &%discard%&. For
is what is wanted for subsequent tests.
+.new
+.vitem &*control&~=&~cutthrough_delivery*&
+.cindex "&ACL;" "cutthrough routing"
+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.
+
+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
+usual fashion. If the item is successfully delivered in cutthrough mode the log line
+is tagged with ">>" rather than "=>" and appears before the acceptance "<="
+line.
+
+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'&>
.cindex "&ACL;" "enabling debug logging"
.cindex "debugging" "enabling from an ACL"
In the main part of the configuration, you put the following definitions:
.code
-domainlist local_domains = my.dom1.example : my.dom2.example
-domainlist relay_domains = friend1.example : friend2.example
-hostlist relay_hosts = 192.168.45.0/24
+domainlist local_domains = my.dom1.example : my.dom2.example
+domainlist relay_to_domains = friend1.example : friend2.example
+hostlist relay_from_hosts = 192.168.45.0/24
.endd
Now you can use these definitions in the ACL that is run for every RCPT
command:
.code
acl_check_rcpt:
- accept domains = +local_domains : +relay_domains
- accept hosts = +relay_hosts
+ accept domains = +local_domains : +relay_to_domains
+ accept hosts = +relay_from_hosts
.endd
The first statement accepts any RCPT command that contains an address in
the local or relay domains. For any other domain, control passes to the second
If the remote server advertises support for the STARTTLS command, and Exim
was built to support TLS encryption, it tries to start a TLS session unless the
server matches &%hosts_avoid_tls%&. See chapter &<<CHAPTLS>>& for more details.
+Either a match in that or &%hosts_verify_avoid_tls%& apply when the transport
+is called for verification.
If the remote server advertises support for the AUTH command, Exim scans
the authenticators configuration for any suitable client settings, as described
git://git.exim.org / exim.git / blobdiff