X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/c45dd1801a10dc40580d422218ae8bfcd7128fc8..f85ae6bda4fced49950c61b29c27ab6aa5732f2f:/doc/doc-docbook/spec.xfpt diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index ed9b0d710..11381a5b8 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -8536,6 +8536,13 @@ start of a portion of the string that is interpreted and replaced as described below in section &<>& onwards. Backslash is used as an escape character, as described in the following section. +Whether a string is expanded depends upon the context. Usually this is solely +dependent upon the option for which a value is sought; in this documentation, +options for which string expansion is performed are marked with † after +the data type. ACL rules always expand strings. A couple of expansion +conditions do not expand some of the brace-delimited branches, for security +reasons. + .section "Literal text in expanded strings" "SECTlittext" @@ -9748,11 +9755,13 @@ dotted-quad decimal form, while for IPv6 addreses the result is in dotted-nibble hexadecimal form. In both cases, this is the "natural" form for DNS. For example, .code -${reverse_ip:192.0.2.4} and ${reverse_ip:2001:0db8:c42:9:1:abcd:192.0.2.3} +${reverse_ip:192.0.2.4} +${reverse_ip:2001:0db8:c42:9:1:abcd:192.0.2.3} .endd returns .code -4.2.0.192 and 3.0.2.0.0.0.0.c.d.c.b.a.1.0.0.0.9.0.0.0.2.4.c.0.8.b.d.0.1.0.0.2 +4.2.0.192 +3.0.2.0.0.0.0.c.d.c.b.a.1.0.0.0.9.0.0.0.2.4.c.0.8.b.d.0.1.0.0.2 .endd @@ -9917,6 +9926,10 @@ lower case), signifying multiplication by 1024 or 1024*1024, respectively. As a special case, the numerical value of an empty string is taken as zero. +In all cases, a relative comparator OP is testing if <&'string1'&> OP +<&'string2'&>; the above example is checking if &$message_size$& is larger than +10M, not if 10M is larger than &$message_size$&. + .vitem &*bool&~{*&<&'string'&>&*}*& .cindex "expansion" "boolean parsing" @@ -11877,6 +11890,25 @@ the value of the Distinguished Name of the certificate is made available in the value is retained during message delivery, except during outbound SMTP deliveries. +.new +.vitem &$tls_sni$& +.vindex "&$tls_sni$&" +.cindex "TLS" "Server Name Indication" +When a TLS session is being established, if the client sends the Server +Name Indication extension, the value will be placed in this variable. +If the variable appears in &%tls_certificate%& then this option and +&%tls_privatekey%& will be re-expanded early in the TLS session, to permit +a different certificate to be presented (and optionally a different key to be +used) to the client, based upon the value of the SNI extension. + +The value will be retained for the lifetime of the message. During outbound +SMTP deliveries, it reflects the value of the &%tls_sni%& option on +the transport. + +This is currently only available when using OpenSSL, built with support for +SNI. +.wen + .vitem &$tod_bsdinbox$& .vindex "&$tod_bsdinbox$&" The time of day and the date, in the format required for BSD-style mailbox @@ -14322,16 +14354,12 @@ harm. This option overrides the &%pipe_as_creator%& option of the &(pipe)& transport driver. -.option openssl_options main "string list" +dont_insert_empty_fragments +.option openssl_options main "string list" unset .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, -each one to be +added or -subtracted from the current value. The default -value is one option which happens to have been set historically. You can -remove all options with: -.code -openssl_options = -all -.endd +each one to be +added or -subtracted from the current value. + This option is only available if Exim is built against OpenSSL. The values available for this option vary according to the age of your OpenSSL install. The &"all"& value controls a subset of flags which are available, typically @@ -14343,14 +14371,78 @@ names lose the leading &"SSL_OP_"& and are lower-cased. Note that adjusting the options can have severe impact upon the security of SSL as used by Exim. It is possible to disable safety checks and shoot yourself in the foot in various unpleasant ways. This option should not be -adjusted lightly. An unrecognised item will be detected at by invoking Exim -with the &%-bV%& flag. +adjusted lightly. An unrecognised item will be detected at startup, by +invoking Exim with the &%-bV%& flag. + +.new +Historical note: prior to release 4.78, 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 -openssl_options = -all +microsoft_big_sslv3_buffer +# Make both old MS and old Eudora happy: +openssl_options = -all +microsoft_big_sslv3_buffer \ + +dont_insert_empty_fragments .endd +Possible options may include: +.ilist +&`all`& +.next +&`allow_unsafe_legacy_renegotiation`& +.next +&`cipher_server_preference`& +.next +&`dont_insert_empty_fragments`& +.next +&`ephemeral_rsa`& +.next +&`legacy_server_connect`& +.next +&`microsoft_big_sslv3_buffer`& +.next +&`microsoft_sess_id_bug`& +.next +&`msie_sslv2_rsa_padding`& +.next +&`netscape_challenge_bug`& +.next +&`netscape_reuse_cipher_change_bug`& +.next +&`no_compression`& +.next +&`no_session_resumption_on_renegotiation`& +.next +&`no_sslv2`& +.next +&`no_sslv3`& +.next +&`no_ticket`& +.next +&`no_tlsv1`& +.next +&`no_tlsv1_1`& +.next +&`no_tlsv1_2`& +.next +&`single_dh_use`& +.next +&`single_ecdh_use`& +.next +&`ssleay_080_client_dh_bug`& +.next +&`sslref2_reuse_cert_type_bug`& +.next +&`tls_block_padding_bug`& +.next +&`tls_d5_bug`& +.next +&`tls_rollback_bug`& +.endlist + .option oracle_servers main "string list" unset .cindex "Oracle" "server list" @@ -15540,6 +15632,12 @@ receiving incoming messages as a server. If you want to supply certificates for 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$& and Exim is built against OpenSSL, then +if the OpenSSL build supports TLS extensions and the TLS client sends the +Server Name Indication extension, then this option and &%tls_privatekey%& +will be re-expanded. +.wen .option tls_crl main string&!! unset .cindex "TLS" "server certificate revocation list" @@ -15572,6 +15670,11 @@ the expansion is forced to fail, or the result is an empty string, the private key is assumed to be in the same file as the server's certificates. See chapter &<>& for further details. +.new +See &%tls_certificate%& discussion of &$tls_sni$& for when this option may be +re-expanded. +.wen + .option tls_remember_esmtp main boolean false .cindex "TLS" "esmtp state; remembering" @@ -22284,6 +22387,20 @@ ciphers is a preference order. +.new +.option tls_sni smtp string&!! unset +.cindex "TLS" "Server Name Indication" +.vindex "&$tls_sni$&" +If this option is set then it sets the $tls_sni variable and causes any +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. + +OpenSSL only, also requiring a build of OpenSSL that supports TLS extensions. +.wen + + + .option tls_tempfail_tryclear smtp boolean true .cindex "4&'xx'& responses" "to STARTTLS" When the server host is not in &%hosts_require_tls%&, and there is a problem in @@ -24048,9 +24165,10 @@ login: server_prompts = Username:: : Password:: server_condition = ${if and{{ \ !eq{}{$auth1} }{ \ - ldapauth{user="cn=${quote_ldap_dn:$auth1},ou=people,o=example.org" \ - pass=${quote:$auth2} \ - ldap://ldap.example.org/} }} } + ldapauth{\ + user="uid=${quote_ldap_dn:$auth1},ou=people,o=example.org" \ + pass=${quote:$auth2} \ + ldap://ldap.example.org/} }} } server_set_id = uid=$auth1,ou=people,o=example.org .endd We have to check that the username is not empty before using it, because LDAP @@ -27709,14 +27827,14 @@ in the MAIL ACL. Subsequent connections from the same client will check this new rate. .code acl_check_connect: - deny ratelimit = 100 / 5m / readonly - log_message = RATE CHECK: $sender_rate/$sender_rate_period \ - (max $sender_rate_limit) + deny ratelimit = 100 / 5m / readonly + log_message = RATE CHECK: $sender_rate/$sender_rate_period \ + (max $sender_rate_limit) # ... acl_check_mail: - warn ratelimit = 100 / 5m / strict - log_message = RATE UPDATE: $sender_rate/$sender_rate_period \ - (max $sender_rate_limit) + warn ratelimit = 100 / 5m / strict + log_message = RATE UPDATE: $sender_rate/$sender_rate_period \ + (max $sender_rate_limit) .endd If Exim encounters multiple &%ratelimit%& conditions with the same key when @@ -33068,6 +33186,7 @@ selection marked by asterisks: &` tls_certificate_verified `& certificate verification status &`*tls_cipher `& TLS cipher suite on <= and => lines &` tls_peerdn `& TLS peer DN on <= and => lines +&` tls_sni `& TLS SNI on <= lines &` unknown_in_list `& DNS lookup failed in list match &` all `& all of the above @@ -33363,6 +33482,12 @@ connection, the cipher suite used is added to the log line, preceded by X=. connection, and a certificate is supplied by the remote host, the peer DN is added to the log line, preceded by DN=. .next +.cindex "log" "TLS SNI" +.cindex "TLS" "logging SNI" +&%tls_sni%&: When a message is received over an encrypted connection, and +the remote host provided the Server Name Indication extension, the SNI is +added to the log line, preceded by SNI=. +.next .cindex "log" "DNS failure in list" &%unknown_in_list%&: This setting causes a log entry to be written when the result of a list match is failure because a DNS lookup failed. @@ -35167,10 +35292,15 @@ unqualified domain &'foundation'&. . //////////////////////////////////////////////////////////////////////////// . //////////////////////////////////////////////////////////////////////////// -.chapter "Support for DKIM (DomainKeys Identified Mail) - RFC4871" "CHID12" &&& +.chapter "Support for DKIM (DomainKeys Identified Mail)" "CHID12" &&& "DKIM Support" .cindex "DKIM" +DKIM is a mechanism by which messages sent by some entity can be provably +linked to a domain which that entity controls. It permits reputation to +be tracked on a per-domain basis, rather than merely upon source IP address. +DKIM is documented in RFC 4871. + Since version 4.70, DKIM support is compiled into Exim by default. It can be disabled by setting DISABLE_DKIM=yes in Local/Makefile. @@ -35191,9 +35321,12 @@ Exim's standard controls. Please note that verification of DKIM signatures in incoming mail is turned on by default for logging purposes. For each signature in incoming email, exim will log a line displaying the most important signature details, and the -signature status. Here is an example: +signature status. Here is an example (with line-breaks added for clarity): .code -2009-09-09 10:22:28 1MlIRf-0003LU-U3 DKIM: d=facebookmail.com s=q1-2009b c=relaxed/relaxed a=rsa-sha1 i=@facebookmail.com t=1252484542 [verification succeeded] +2009-09-09 10:22:28 1MlIRf-0003LU-U3 DKIM: + d=facebookmail.com s=q1-2009b + c=relaxed/relaxed a=rsa-sha1 + i=@facebookmail.com t=1252484542 [verification succeeded] .endd You might want to turn off DKIM verification processing entirely for internal or relay mail sources. To do that, set the &%dkim_disable_verify%& ACL @@ -35401,7 +35534,7 @@ for a match against the domain or identity that the ACL is currently verifying verb to a group of domains or identities. For example: .code -# Warn when message apparently from GMail has no signature at all +# Warn when Mail purportedly from GMail has no signature at all warn log_message = GMail sender without DKIM signature sender_domains = gmail.com dkim_signers = gmail.com @@ -35411,10 +35544,10 @@ warn log_message = GMail sender without DKIM signature .vitem &%dkim_status%& ACL condition that checks a colon-separated list of possible DKIM verification results agains the actual result of verification. This is typically used -to restrict an ACL verb to a list of verification outcomes, like: +to restrict an ACL verb to a list of verification outcomes, for example: .code -deny message = Message from Paypal with invalid or missing signature +deny message = Mail from Paypal with invalid/missing signature sender_domains = paypal.com:paypal.de dkim_signers = paypal.com:paypal.de dkim_status = none:invalid:fail