X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/2c47372fad0f829ddfa29d04095f57a70206469c..c679ee08b006c8fe4c62b353d909c992a725fc11:/doc/doc-docbook/spec.xfpt?ds=sidebyside diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index aa6da73d3..585f5e310 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -3162,6 +3162,10 @@ If invoked by an admin user, then &%macro%&, &%macro_list%& and &%macros%& are available, similarly to the drivers. Because macros are sometimes used for storing passwords, this option is restricted. The output format is one item per line. +.new +For the "-bP macro " form, if no such macro is found +the exit status will be nonzero. +.wen .vitem &%-bp%& .oindex "&%-bp%&" @@ -5579,19 +5583,27 @@ Another two commented-out option settings follow: .cindex "port" "465 and 587" .cindex "port" "for message submission" .cindex "message" "submission, ports for" -.cindex "ssmtp protocol" +.cindex "submissions protocol" .cindex "smtps protocol" +.cindex "ssmtp protocol" +.cindex "SMTP" "submissions protocol" .cindex "SMTP" "ssmtp protocol" .cindex "SMTP" "smtps protocol" These options provide better support for roaming users who wish to use this server for message submission. They are not much use unless you have turned on TLS (as described in the previous paragraph) and authentication (about which -more in section &<>&). The usual SMTP port 25 is often blocked -on end-user networks, so RFC 4409 specifies that message submission should use -port 587 instead. However some software (notably Microsoft Outlook) cannot be -configured to use port 587 correctly, so these settings also enable the -non-standard &"smtps"& (aka &"ssmtp"&) port 465 (see section -&<>&). +more in section &<>&). +Mail submission from mail clients (MUAs) should be separate from inbound mail +to your domain (MX delivery) for various good reasons (eg, ability to impose +much saner TLS protocol and ciphersuite requirements without unintended +consequences). +RFC 6409 (previously 4409) specifies use of port 587 for SMTP Submission, +which uses STARTTLS, so this is the &"submission"& port. +RFC 8314 specifies use of port 465 as the &"submissions"& protocol, +which should be used in preference to 587. +You should also consider deploying SRV records to help clients find +these ports. +Older names for &"submissions"& are &"smtps"& and &"ssmtp"&. Two more commented-out options settings follow: .code @@ -7827,6 +7839,17 @@ ${lookup redis{set keyname ${quote_redis:objvalue plus}}} ${lookup redis{get keyname}} .endd +As of release 4.91, "lightweight" support for Redis Cluster is available. +Requires &%redis_servers%& list to contain all the servers in the cluster, all +of which must be reachable from the running exim instance. If the cluster has +master/slave replication, the list must contain all the master and slave +servers. + +When the Redis Cluster returns a "MOVED" response to a query, exim does not +immediately follow the redirection but treats the response as a DEFER, moving on +to the next server in the &%redis_servers%& list until the correct server is +reached. + .ecindex IIDfidalo1 .ecindex IIDfidalo2 @@ -9125,6 +9148,31 @@ the expansion result is an empty string. If the ACL returns defer the result is a forced-fail. Otherwise the expansion fails. +.new +.vitem "&*${authresults{*&<&'authserv-id'&>&*}}*&" +.cindex authentication "results header" +.cindex headers "authentication-results:" +This item returns a string suitable for insertion as an +&'Authentication-Results"'& +header line. +The given <&'authserv-id'&> is included in the result; typically this +will ba a domain name identifying the system performing the authentications. +Methods that may be present in the result include: +.code +none +iprev +auth +spf +dkim +.endd + +Example use (as an ACL modifier): +.code + add_header = :at_start:${authresults {$primary_hostname}} +.endd +.wen + + .vitem "&*${certextract{*&<&'field'&>&*}{*&<&'certificate'&>&*}&&& {*&<&'string2'&>&*}{*&<&'string3'&>&*}}*&" .cindex "expansion" "extracting certificate fields" @@ -9337,7 +9385,7 @@ item in a new list; if the condition is false, the item is discarded. The separator used for the output list is the same as the one used for the input, but a separator setting is not included in the output. For example: .code -${filter{a:b:c}{!eq{$item}{b}} +${filter{a:b:c}{!eq{$item}{b}}} .endd yields &`a:c`&. At the end of the expansion, the value of &$item$& is restored to what it was before. See also the &*map*& and &*reduce*& expansion items. @@ -10637,7 +10685,11 @@ the output length. Values of 224, 256, 384 and 512 are accepted; with 256 being the default. The &%sha3%& expansion item is only supported if Exim has been -compiled with GnuTLS 3.5.0 or later. +compiled with GnuTLS 3.5.0 or later, +.new +or OpenSSL 1.1.1 or later. +The macro "_CRYPTO_HASH_SHA3" will be defined if it is supported. +.wen .vitem &*${stat:*&<&'string'&>&*}*& @@ -11659,7 +11711,7 @@ contain the trailing slash. If &$config_file$& does not contain a slash, .vindex "&$config_file$&" The name of the main configuration file Exim is using. -.vitem &$dkim_verify_status$& &&& +.vitem &$dkim_verify_status$& Results of DKIM verification. For details see section &<>&. @@ -12969,6 +13021,10 @@ and then set to the outgoing cipher suite if one is negotiated. See chapter &<>& for details of TLS support and chapter &<>& for details of the &(smtp)& transport. +.vitem &$tls_out_dane$& +.vindex &$tls_out_dane$& +DANE active status. See section &<>&. + .vitem &$tls_in_ocsp$& .vindex "&$tls_in_ocsp$&" When a message is received from a remote client connection @@ -13034,6 +13090,10 @@ During outbound SMTP deliveries, this variable reflects the value of the &%tls_sni%& option on the transport. +.vitem &$tls_out_tlsa_usage$& +.vindex &$tls_out_tlsa_usage$& +Bitfield of TLSA record types found. See section &<>&. + .vitem &$tod_bsdinbox$& .vindex "&$tod_bsdinbox$&" The time of day and the date, in the format required for BSD-style mailbox @@ -13408,23 +13468,32 @@ value of &%daemon_smtp_ports%& is no longer relevant in this example.) -.section "Support for the obsolete SSMTP (or SMTPS) protocol" "SECTsupobssmt" +.section "Support for the submissions (aka SSMTP or SMTPS) protocol" "SECTsupobssmt" +.cindex "submissions protocol" .cindex "ssmtp protocol" .cindex "smtps protocol" .cindex "SMTP" "ssmtp protocol" .cindex "SMTP" "smtps protocol" -Exim supports the obsolete SSMTP protocol (also known as SMTPS) that was used -before the STARTTLS command was standardized for SMTP. Some legacy clients -still use this protocol. If the &%tls_on_connect_ports%& option is set to a -list of port numbers or service names, -connections to those ports must use SSMTP. The most -common use of this option is expected to be +Exim supports the use of TLS-on-connect, used by mail clients in the +&"submissions"& protocol, historically also known as SMTPS or SSMTP. +For some years, IETF Standards Track documents only blessed the +STARTTLS-based Submission service (port 587) while common practice was to support +the same feature set on port 465, but using TLS-on-connect. +If your installation needs to provide service to mail clients +(Mail User Agents, MUAs) then you should provide service on both the 587 and +the 465 TCP ports. + +If the &%tls_on_connect_ports%& option is set to a list of port numbers or +service names, connections to those ports must first establish TLS, before +proceeding to the application layer use of the SMTP protocol. + +The common use of this option is expected to be .code tls_on_connect_ports = 465 .endd -because 465 is the usual port number used by the legacy clients. There is also -a command line option &%-tls-on-connect%&, which forces all ports to behave in -this way when a daemon is started. +per RFC 8314. +There is also a command line option &%-tls-on-connect%&, which forces all ports +to behave in this way when a daemon is started. &*Warning*&: Setting &%tls_on_connect_ports%& does not of itself cause the daemon to listen on those ports. You must still specify them in @@ -14693,6 +14762,7 @@ 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" +.cindex DNS "IPv6 disabling" When Exim is compiled with IPv6 support and &%disable_ipv6%& is not set, it looks for IPv6 address records (AAAA records) as well as IPv4 address records (A records) when trying to find IP addresses for hosts, unless the host's @@ -16898,8 +16968,8 @@ and any external programs which are passed a reference to a message data file will need to be aware of the potential different format. Using any of the ACL conditions noted will negate the reception benefit -(as a Unix-mbox-format file is contructed for them). -The transimssion benefit is maintained. +(as a Unix-mbox-format file is constructed for them). +The transmission benefit is maintained. .option sqlite_lock_timeout main time 5s .cindex "sqlite lookup type" "lock timeout" @@ -17126,7 +17196,7 @@ option in the relevant &(smtp)& transport. separator in the usual way to avoid confusion under IPv6. &*Note*&: Under current versions of OpenSSL, when a list of more than one -file is used, the &$tls_in_ourcert$& veriable is unreliable. +file is used, the &$tls_in_ourcert$& variable is unreliable. &*Note*&: OCSP stapling is not usable under OpenSSL when a list of more than one file is used. @@ -18745,7 +18815,9 @@ records. MX records of equal priority are sorted by Exim into a random order. Exim then looks for address records for the host names obtained from MX or SRV records. When a host has more than one IP address, they are sorted into a random order, -except that IPv6 addresses are always sorted before IPv4 addresses. If all the +.new +except that IPv6 addresses are sorted before IPv4 addresses. If all the +.wen IP addresses found are discarded by a setting of the &%ignore_target_hosts%& generic option, the router declines. @@ -18878,6 +18950,24 @@ However, it will result in any message with mistyped domains also being queued. +.new +.option ipv4_only "string&!!" unset +.cindex IPv6 disabling +.cindex DNS "IPv6 disabling" +The string is expanded, and if the result is anything but a forced failure, +or an empty string, or one of the strings “0” or “no” or “false” +(checked without regard to the case of the letters), +only A records are used. + +.option ipv4_prefer "string&!!" unset +.cindex IPv4 preference +.cindex DNS "IPv4 preference" +The string is expanded, and if the result is anything but a forced failure, +or an empty string, or one of the strings “0” or “no” or “false” +(checked without regard to the case of the letters), +A records are sorted before AAAA records (inverting the default). +.wen + .option mx_domains dnslookup "domain list&!!" unset .cindex "MX record" "required to exist" .cindex "SRV record" "required to exist" @@ -19482,8 +19572,8 @@ whether obtained from an MX lookup or not. .section "How the options are used" "SECThowoptused" -The options are a sequence of words; in practice no more than three are ever -present. One of the words can be the name of a transport; this overrides the +The options are a sequence of words, space-separated. +One of the words can be the name of a transport; this overrides the &%transport%& option on the router for this particular routing rule only. The other words (if present) control randomization of the list of hosts on a per-rule basis, and how the IP addresses of the hosts are to be found when @@ -19503,6 +19593,12 @@ also look in &_/etc/hosts_& or other sources of information. &%bydns%&: look up address records for the hosts directly in the DNS; fail if no address records are found. If there is a temporary DNS error (such as a timeout), delivery is deferred. +.new +.next +&%ipv4_only%&: in direct DNS lookups, look up only A records. +.next +&%ipv4_prefer%&: in direct DNS lookups, sort A records before AAAA records. +.wen .endlist For example: @@ -24149,6 +24245,17 @@ Exim will request a Certificate Status on a TLS session for any host that matches this list. &%tls_verify_certificates%& should also be set for the transport. +.new +.option hosts_require_dane smtp "host list&!!" unset +.cindex DANE "transport options" +.cindex DANE "requiring for certain servers" +If built with DANE support, Exim will require that a DNSSEC-validated +TLSA record is present for any host matching the list, +and that a DANE-verified TLS connection is made. +There will be no fallback to in-clear communication. +See section &<>&. +.wen + .option hosts_require_ocsp smtp "host list&!!" unset .cindex "TLS" "requiring for certain servers" Exim will request, and check for a valid Certificate Status being given, on a @@ -24178,6 +24285,18 @@ This option provides a list of servers to which, provided they announce CHUNKING support, Exim will attempt to use BDAT commands rather than DATA. BDAT will not be used in conjunction with a transport filter. +.new +.option hosts_try_dane smtp "host list&!!" unset +.cindex DANE "transport options" +.cindex DANE "attempting for certain servers" +If built with DANE support, Exim will lookup a +TLSA record for any host matching the list. +If found and verified by DNSSEC, +a DANE-verified TLS connection is made to that host; +there will be no fallback to in-clear communication. +See section &<>&. +.wen + .option hosts_try_fastopen smtp "host list&!!" unset .cindex "fast open, TCP" "enabling, in client" .cindex "TCP Fast Open" "enabling, in client" @@ -24195,7 +24314,7 @@ as the initiator must present a cookie in the SYN segment. On (at least some) current Linux distributions the facility must be enabled in the kernel by the sysadmin before the support is usable. There is no option for control of the server side; if the system supports -it it is always enebled. Note that legthy operations in the connect ACL, +it it is always enabled. Note that lengthy operations in the connect ACL, such as DNSBL lookups, will still delay the emission of the SMTP banner. .option hosts_try_prdr smtp "host list&!!" * @@ -27057,22 +27176,36 @@ in order to get TLS to work. -.section "Support for the legacy &""ssmtp""& (aka &""smtps""&) protocol" &&& +.section "Support for the &""submissions""& (aka &""ssmtp""& and &""smtps""&) protocol" &&& "SECID284" +.cindex "submissions protocol" .cindex "ssmtp protocol" .cindex "smtps protocol" +.cindex "SMTP" "submissions protocol" .cindex "SMTP" "ssmtp protocol" .cindex "SMTP" "smtps protocol" -Early implementations of encrypted SMTP used a different TCP port from normal -SMTP, and expected an encryption negotiation to start immediately, instead of -waiting for a STARTTLS command from the client using the standard SMTP -port. The protocol was called &"ssmtp"& or &"smtps"&, and port 465 was -allocated for this purpose. - -This approach was abandoned when encrypted SMTP was standardized, but there are -still some legacy clients that use it. Exim supports these clients by means of -the &%tls_on_connect_ports%& global option. Its value must be a list of port -numbers; the most common use is expected to be: +The history of port numbers for TLS in SMTP is a little messy and has been +contentious. As of RFC 8314, the common practice of using the historically +allocated port 465 for "email submission but with TLS immediately upon connect +instead of using STARTTLS" is officially blessed by the IETF, and recommended +in preference to STARTTLS. + +The name originally assigned to the port was &"ssmtp"& or &"smtps"&, but as +clarity emerged over the dual roles of SMTP, for MX delivery and Email +Submission, nomenclature has shifted. The modern name is now &"submissions"&. + +This approach was, for a while, officially abandoned when encrypted SMTP was +standardized, but many clients kept using it, even as the TCP port number was +reassigned for other use. +Thus you may encounter guidance claiming that you shouldn't enable use of +this port. +In practice, a number of mail-clients have only supported submissions, not +submission with STARTTLS upgrade. +Ideally, offer both submission (587) and submissions (465) service. + +Exim supports TLS-on-connect by means of the &%tls_on_connect_ports%& +global option. Its value must be a list of port numbers; +the most common use is expected to be: .code tls_on_connect_ports = 465 .endd @@ -27084,7 +27217,7 @@ an extra port &-- rather, it specifies different behaviour on a port that is defined elsewhere. There is also a &%-tls-on-connect%& command line option. This overrides -&%tls_on_connect_ports%&; it forces the legacy behaviour for all ports. +&%tls_on_connect_ports%&; it forces the TLS-only behaviour for all ports. @@ -27363,8 +27496,8 @@ tls_require_ciphers = ${if =={$received_port}{25}\ When Exim has been built with TLS support, it advertises the availability of the STARTTLS command to client hosts that match &%tls_advertise_hosts%&, but not to any others. The default value of this option is *, which means -that STARTTLS is alway advertised. Set it to blank to never advertise; -this is reasonble for systems that want to use TLS only as a client. +that STARTTLS is always advertised. Set it to blank to never advertise; +this is reasonable for systems that want to use TLS only as a client. If STARTTLS is to be used you need to set some other options in order to make TLS available. @@ -27797,7 +27930,7 @@ unencrypted data stream from and to the delivery processes. An older mode of operation can be enabled on a per-host basis by the &%hosts_noproxy_tls%& option on the &(smtp)& transport. If the host matches -this list the proxy process descibed above is not used; instead Exim +this list the proxy process described above is not used; instead Exim shuts down an existing TLS session being run by the delivery process before passing the socket to a new process. The new process may then try to start a new TLS session, and if successful, may try to re-authenticate @@ -27920,6 +28053,133 @@ Open-source PKI book, available online at +.new +.section DANE "SECDANE" +.cindex DANE +DNS-based Authentication of Named Entities, as applied to SMTP over TLS, provides assurance to a client that +it is actually talking to the server it wants to rather than some attacker operating a Man In The Middle (MITM) +operation. The latter can terminate the TLS connection you make, and make another one to the server (so both +you and the server still think you have an encrypted connection) and, if one of the "well known" set of +Certificate Authorities has been suborned - something which *has* been seen already (2014), a verifiable +certificate (if you're using normal root CAs, eg. the Mozilla set, as your trust anchors). + +What DANE does is replace the CAs with the DNS as the trust anchor. The assurance is limited to a) the possibility +that the DNS has been suborned, b) mistakes made by the admins of the target server. The attack surface presented +by (a) is thought to be smaller than that of the set of root CAs. + +It also allows the server to declare (implicitly) that connections to it should use TLS. An MITM could simply +fail to pass on a server's STARTTLS. + +DANE scales better than having to maintain (and side-channel communicate) copies of server certificates +for every possible target server. It also scales (slightly) better than having to maintain on an SMTP +client a copy of the standard CAs bundle. It also means not having to pay a CA for certificates. + +DANE requires a server operator to do three things: 1) run DNSSEC. This provides assurance to clients +that DNS lookups they do for the server have not been tampered with. The domain MX record applying +to this server, its A record, its TLSA record and any associated CNAME records must all be covered by +DNSSEC. +2) add TLSA DNS records. These say what the server certificate for a TLS connection should be. +3) offer a server certificate, or certificate chain, in TLS connections which is traceable to the one +defined by (one of?) the TSLA records + +There are no changes to Exim specific to server-side operation of DANE. +Support for client-side operation of DANE can be included at compile time by defining SUPPORT_DANE=yes +in &_Local/Makefile_&. +If it has been included, the macro "_HAVE_DANE" will be defined. + +The TLSA record for the server may have "certificate usage" of DANE-TA(2) or DANE-EE(3). The latter specifies +the End Entity directly, i.e. the certificate involved is that of the server (and should be the sole one transmitted +during the TLS handshake); this is appropriate for a single system, using a self-signed certificate. +DANE-TA usage is effectively declaring a specific CA to be used; this might be a private CA or a public, +well-known one. A private CA at simplest is just a self-signed certificate which is used to sign +cerver certificates, but running one securely does require careful arrangement. If a private CA is used +then either all clients must be primed with it, or (probably simpler) the server TLS handshake must transmit +the entire certificate chain from CA to server-certificate. If a public CA is used then all clients must be primed with it +(losing one advantage of DANE) - but the attack surface is reduced from all public CAs to that single CA. +DANE-TA is commonly used for several services and/or servers, each having a TLSA query-domain CNAME record, +all of which point to a single TLSA record. + +The TLSA record should have a Selector field of SPKI(1) and a Matching Type field of SHA2-512(2). + +At the time of writing, &url(https://www.huque.com/bin/gen_tlsa) +is useful for quickly generating TLSA records; and commands like + +.code + openssl x509 -in -pubkey -noout /dev/null \ + | openssl sha512 \ + | awk '{print $2}' +.endd + +are workable for 4th-field hashes. + +For use with the DANE-TA model, server certificates must have a correct name (SubjectName or SubjectAltName). + +The use of OCSP-stapling should be considered, allowing for fast revocation of certificates (which would otherwise +be limited by the DNS TTL on the TLSA records). However, this is likely to only be usable with DANE-TA. NOTE: the +default of requesting OCSP for all hosts is modified iff DANE is in use, to: + +.code + hosts_request_ocsp = ${if or { {= {0}{$tls_out_tlsa_usage}} \ + {= {4}{$tls_out_tlsa_usage}} } \ + {*}{}} +.endd + +The (new) variable &$tls_out_tlsa_usage$& is a bitfield with numbered bits set for TLSA record usage codes. +The zero above means DANE was not in use, the four means that only DANE-TA usage TLSA records were +found. If the definition of &%hosts_request_ocsp%& includes the +string "tls_out_tlsa_usage", they are re-expanded in time to +control the OCSP request. + +This modification of hosts_request_ocsp is only done if it has the default value of "*". Admins who change it, and +those who use &%hosts_require_ocsp%&, should consider the interaction with DANE in their OCSP settings. + + +For client-side DANE there are two new smtp transport options, &%hosts_try_dane%& and &%hosts_require_dane%&. +The latter variant will result in failure if the target host is not DNSSEC-secured. + +DANE will only be usable if the target host has DNSSEC-secured MX, A and TLSA records. + +A TLSA lookup will be done if either of the above options match and the host-lookup succeeded using dnssec. +If a TLSA lookup is done and succeeds, a DANE-verified TLS connection +will be required for the host. If it does not, the host will not +be used; there is no fallback to non-DANE or non-TLS. + +If DANE is requested and useable (see above) the following transport options are ignored: +.code + hosts_require_tls + tls_verify_hosts + tls_try_verify_hosts + tls_verify_certificates + tls_crl + tls_verify_cert_hostnames +.endd + +If DANE is not usable, whether requested or not, and CA-anchored +verification evaluation is wanted, the above variables should be set appropriately. + +Currently the &%dnssec_request_domains%& must be active and &%dnssec_require_domains%& is ignored. + +If verification was successful using DANE then the "CV" item in the delivery log line will show as "CV=dane". + +There is a new variable &$tls_out_dane$& which will have "yes" if +verification succeeded using DANE and "no" otherwise (only useful +in combination with events; see &<>&), +and a new variable &$tls_out_tlsa_usage$& (detailed above). + +.cindex DANE reporting +An event (see &<>&) of type "dane:fail" will be raised on failures +to achieve DANE-verified connection, if one was either requested and offered, or +required. This is intended to support TLS-reporting as defined in +&url(https://tools.ietf.org/html/draft-ietf-uta-smtp-tlsrpt-17). +The &$event_data$& will be one of the Result Types defined in +Section 4.3 of that document. + +Under GnuTLS, DANE is only supported from version 3.0.0 onwards. +.wen + + + . //////////////////////////////////////////////////////////////////////////// . //////////////////////////////////////////////////////////////////////////// @@ -28244,8 +28504,8 @@ acl_smtp_rcpt = ${if ={25}{$interface_port} \ {acl_check_rcpt} {acl_check_rcpt_submit} } .endd In the default configuration file there are some example settings for -providing an RFC 4409 message submission service on port 587 and a -non-standard &"smtps"& service on port 465. You can use a string +providing an RFC 4409 message &"submission"& service on port 587 and +an RFC 8314 &"submissions"& service on port 465. You can use a string expansion like this to choose an ACL for MUAs on these ports which is more appropriate for this purpose than the default ACL on port 25. @@ -31073,7 +31333,7 @@ This option applies to recipient callouts only. For example: .code require verify = recipient/callout=use_sender,hold .endd -It causes the connection to be helod open and used for any further recipients +It causes the connection to be held open and used for any further recipients and for eventual delivery (should that be done quickly). Doing this saves on TCP and SMTP startup costs, and TLS costs also when that is used for the connections. @@ -31557,9 +31817,9 @@ though individual ones can be included or not at build time: .vitem &%avast%& .cindex "virus scanners" "avast" This is the scanner daemon of Avast. It has been tested with Avast Core -Security (currently at version 1.1.7). -You can get a trial version at &url(http://www.avast.com) or for Linux -at &url(http://www.avast.com/linux-server-antivirus). +Security (currently at version 2.2.0). +You can get a trial version at &url(https://www.avast.com) or for Linux +at &url(https://www.avast.com/linux-server-antivirus). This scanner type takes one option, which can be either a full path to a UNIX socket, or host and port specifiers separated by white space. @@ -31586,6 +31846,8 @@ $ socat UNIX:/var/run/avast/scan.sock STDIO: PACK .endd +Only the first virus detected will be reported. + .vitem &%aveserver%& .cindex "virus scanners" "Kaspersky" @@ -32302,7 +32564,7 @@ All parts contained within an attachment multipart are attachments. As an example, the following will ban &"HTML mail"& (including that sent with alternative plain text), while allowing HTML files to be attached. HTML -coverletter mail attached to non-HMTL coverletter mail will also be allowed: +coverletter mail attached to non-HTML coverletter mail will also be allowed: .code deny message = HTML mail is not accepted here !condition = $mime_is_rfc822 @@ -36077,6 +36339,7 @@ the following table: &` `& on &"Completed"& lines: time spent on queue &`R `& on &`<=`& lines: reference for local bounce &` `& on &`=>`& &`>>`& &`**`& and &`==`& lines: router name +&`RT `& on &`<=`& lines: time taken for reception &`S `& size of message in bytes &`SNI `& server name indication from TLS client hello &`ST `& shadow transport name @@ -36171,7 +36434,7 @@ selection marked by asterisks: &` incoming_interface `& local interface on <= and => lines &` incoming_port `& remote port on <= lines &`*lost_incoming_connection `& as it says (includes timeouts) -&` millisec `& millisecond timestamps and QT,DT,D times +&` millisec `& millisecond timestamps and RT,QT,DT,D times &` outgoing_interface `& local interface on => lines &` outgoing_port `& add remote port to => lines &`*queue_run `& start and end queue runs @@ -36262,7 +36525,7 @@ process is started because &%queue_only%& is set or &%-odq%& was used. &%deliver_time%&: For each delivery, the amount of real time it has taken to perform the actual delivery is logged as DT=<&'time'&>, for example, &`DT=1s`&. If millisecond logging is enabled, short times will be shown with greater -precision, eg. &`DT=0.304`&. +precision, eg. &`DT=0.304s`&. .next .cindex "log" "message size on delivery" .cindex "size" "of message" @@ -36272,7 +36535,7 @@ the &"=>"& line, tagged with S=. .new .cindex log "DKIM verification" .cindex DKIM "verification logging" -&%dkim%&: For message acceptance log lines, when an DKIM signture in the header +&%dkim%&: For message acceptance log lines, when an DKIM signature in the header verifies successfully a tag of DKIM is added, with one of the verified domains. .next .cindex log "DKIM verification" @@ -36351,7 +36614,7 @@ connection is unexpectedly dropped. .next .cindex "log" "millisecond timestamps" .cindex millisecond logging -.cindex timstamps "millisecond, in logs" +.cindex timestamps "millisecond, in logs" &%millisec%&: Timestamps have a period and three decimal places of finer granularity appended to the seconds value. .next @@ -36366,7 +36629,7 @@ followed by IP address in square brackets. You can disable this by turning off the &%outgoing_interface%& option. .next .cindex "log" "outgoing remote port" -.cindex "port" "logging outgoint remote" +.cindex "port" "logging outgoing remote" .cindex "TCP/IP" "logging outgoing remote port" &%outgoing_port%&: The remote port number is added to delivery log lines (those containing => tags) following the IP address. @@ -36400,6 +36663,14 @@ precision, eg. &`QT=1.578s`&. the local host is logged as QT=<&'time'&> on &"Completed"& lines, for example, &`QT=3m45s`&. The clock starts when Exim starts to receive the message, so it includes reception time as well as the total delivery time. +.new +.next +.cindex "log" "receive duration" +&%receive_time%&: For each message, the amount of real time it has taken to +perform the reception is logged as RT=<&'time'&>, for example, &`RT=1s`&. +If millisecond logging is enabled, short times will be shown with greater +precision, eg. &`RT=0.204s`&. +.wen .next .cindex "log" "recipients" &%received_recipients%&: The recipients of a message are listed in the main log @@ -36552,9 +36823,16 @@ specifies whether characters with values greater than 127 should be logged unchanged, or whether they should be rendered as escape sequences. .next .cindex "log" "certificate verification" +.cindex log DANE +.cindex DANE logging &%tls_certificate_verified%&: An extra item is added to <= and => log lines when TLS is in use. The item is &`CV=yes`& if the peer's certificate was -verified, and &`CV=no`& if not. +verified +.new +using a CA trust anchor, +&`CA=dane`& if using a DNS trust anchor, +.wen +and &`CV=no`& if not. .next .cindex "log" "TLS cipher" .cindex "TLS" "logging cipher" @@ -38524,7 +38802,7 @@ There is no dot-stuffing (and no dot-termination). 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. +DKIM is documented in RFC 6376. .new As DKIM relies on the message being unchanged in transit, messages handled @@ -38551,8 +38829,12 @@ In typical Exim style, the verification implementation does not include any default "policy". Instead it enables you to build your own policy using Exim's standard controls. +.new Please note that verification of DKIM signatures in incoming mail is turned -on by default for logging purposes. For each signature in incoming email, +on by default for logging (in the <= line) purposes. + +Additional log detail can be enabled using the &%dkim_verbose%& log_selector. +When set, 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 (with line-breaks added for clarity): .code @@ -38561,6 +38843,8 @@ signature status. Here is an example (with line-breaks added for clarity): c=relaxed/relaxed a=rsa-sha1 i=@facebookmail.com t=1252484542 [verification succeeded] .endd +.wen + 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 control modifier. This should typically be done in the RCPT ACL, at points @@ -38571,6 +38855,23 @@ senders). .section "Signing outgoing messages" "SECDKIMSIGN" .cindex "DKIM" "signing" +.new +For signing to be usable you must have published a DKIM record in DNS. +Note that RFC 8301 says: +.code +rsa-sha1 MUST NOT be used for signing or verifying. + +Signers MUST use RSA keys of at least 1024 bits for all keys. +Signers SHOULD use RSA keys of at least 2048 bits. +.endd + +Note also that the key content (the 'p=' field) +in the DNS record is different between RSA and EC keys; +for the former it is the base64 of the ASN.1 for the RSA public key +(equivalent to the private-key .pem with the header/trailer stripped) +but for EC keys it is the base64 of the pure key; no ASN.1 wrapping. +.wen + Signing is enabled by setting private options on the SMTP transport. These options take (expandable) strings as arguments. @@ -38579,7 +38880,8 @@ The domain(s) you want to sign with. After expansion, this can be a list. Each element in turn is put into the &%$dkim_domain%& expansion variable while expanding the remaining signing options. -If it is empty after expansion, DKIM signing is not done. +If it is empty after expansion, DKIM signing is not done, +and no error will result even if &%dkim_strict%& is set. .option dkim_selector smtp string list&!! unset This sets the key selector string. @@ -38587,7 +38889,8 @@ After expansion, which can use &$dkim_domain$&, this can be a list. Each element in turn is put in the expansion variable &%$dkim_selector%& which may be used in the &%dkim_private_key%& option along with &%$dkim_domain%&. -If the option is empty after expansion, DKIM signing is not done for this domain. +If the option is empty after expansion, DKIM signing is not done for this domain, +and no error will result even if &%dkim_strict%& is set. .option dkim_private_key smtp string&!! unset This sets the private key to use. @@ -38595,20 +38898,47 @@ You can use the &%$dkim_domain%& and &%$dkim_selector%& expansion variables to determine the private key to use. The result can either .ilist -be a valid RSA private key in ASCII armor, including line breaks. +be a valid RSA private key in ASCII armor (.pem file), including line breaks +.new +.next +with GnuTLS 3.6.0 or later, be a valid Ed25519 private key (same format as above) +.wen .next start with a slash, in which case it is treated as a file that contains -the private key. +the private key .next be "0", "false" or the empty string, in which case the message will not be signed. This case will not result in an error, even if &%dkim_strict%& is set. .endlist -If the option is empty after expansion, DKIM signing is not done. + +.new +Note that RFC 8301 says: +.code +Signers MUST use RSA keys of at least 1024 bits for all keys. +Signers SHOULD use RSA keys of at least 2048 bits. +.endd + +Support for EC keys is being developed under +&url(https://datatracker.ietf.org/doc/draft-ietf-dcrup-dkim-crypto/). +They are considerably smaller than RSA keys for equivalent protection. +As they are a recent development, users should consider dual-signing +(by setting a list of selectors, and an expansion for this option) +for some transition period. +The "_CRYPTO_SIGN_ED25519" macro will be defined if support is present +for EC keys. +.wen .option dkim_hash smtp string&!! sha256 Can be set alternatively to &"sha1"& to use an alternate hash -method. Note that sha1 is now condidered insecure, and deprecated. +method. + +.new +Note that RFC 8301 says: +.code +rsa-sha1 MUST NOT be used for signing or verifying. +.endd +.wen .option dkim_identity smtp string&!! unset If set after expansion, the value is used to set an "i=" tag in @@ -38640,7 +38970,7 @@ whether or not each header is present in the message. The default list is available for the expansion in the macro "_DKIM_SIGN_HEADERS". -If a name is repeated, multiple headers by that name (or the absence therof) +If a name is repeated, multiple headers by that name (or the absence thereof) will be signed. The textually later headers in the headers part of the message are signed first, if there are multiples. @@ -38648,7 +38978,7 @@ A name can be prefixed with either an '=' or a '+' character. If an '=' prefix is used, all headers that are present with this name will be signed. If a '+' prefix if used, all headers that are present with this name -will be signed, and one signtature added for a missing header with the +will be signed, and one signature added for a missing header with the name will be appended. @@ -38732,11 +39062,13 @@ This variable can be overwritten using an ACL 'set' modifier. This might, for instance, be done to enforce a policy restriction on hash-method or key-size: .code - warn condition = ${if eq {$dkim_algo}{rsa-sha1}} - condition = ${if eq {$dkim_verify_status}{pass}} + warn condition = ${if eq {$dkim_verify_status}{pass}} + condition = ${if eq {$len_3:$dkim_algo}{rsa}} + condition = ${if or {eq {$dkim_algo}{rsa-sha1}} \ + {< {$dkim_key_length}{1024}} } logwrite = NOTE: forcing dkim verify fail (was pass) set dkim_verify_status = fail - set dkim_verify_reason = hash too weak + set dkim_verify_reason = hash too weak or key too short .endd After all the DKIM ACL runs have completed, the value becomes a @@ -38762,7 +39094,7 @@ re-written or otherwise changed in a way which is incompatible with DKIM verification. It may of course also mean that the signature is forged. .endlist -This variable can be overwritten using an ACL 'set' modifier. +This variable can be overwritten, with any value, using an ACL 'set' modifier. .vitem &%$dkim_domain%& The signing domain. IMPORTANT: This variable is only populated if there is @@ -38779,6 +39111,24 @@ The key record selector string. .vitem &%$dkim_algo%& The algorithm used. One of 'rsa-sha1' or 'rsa-sha256'. +.new +If running under GnuTLS 3.6.0 or later, may also be 'ed25519-sha256'. +The "_CRYPTO_SIGN_ED25519" macro will be defined if support is present +for EC keys. +.wen + +.new +Note that RFC 8301 says: +.code +rsa-sha1 MUST NOT be used for signing or verifying. + +DKIM signatures identified as having been signed with historic +algorithms (currently, rsa-sha1) have permanently failed evaluation +.endd + +To enforce this you must have a DKIM ACL which checks this variable +and overwrites the &$dkim_verify_status$& variable as discussed above. +.wen .vitem &%$dkim_canon_body%& The body canonicalization method. One of 'relaxed' or 'simple'. @@ -38807,6 +39157,9 @@ UNIX timestamp reflecting the date and time when the signer wants the signature to be treated as "expired". When this was not specified by the signer, "9999999999999" is returned. This makes it possible to do useful integer size comparisons against this value. +.new +Note that Exim does not check this value. +.wen .vitem &%$dkim_headernames%& A colon-separated list of names of headers included in the signature. @@ -38830,6 +39183,19 @@ Notes from the key record (tag n=). .vitem &%$dkim_key_length%& Number of bits in the key. + +.new +Note that RFC 8301 says: +.code +Verifiers MUST NOT consider signatures using RSA keys of +less than 1024 bits as valid signatures. +.endd + +To enforce this you must have a DKIM ACL which checks this variable +and overwrites the &$dkim_verify_status$& variable as discussed above. +As EC keys are much smaller, the check should only do this for RSA keys. +.wen + .endlist In addition, two ACL conditions are provided: @@ -39202,7 +39568,7 @@ This will add a component tagged with &"PRX="& to the line. .cindex internationalisation "email address" .cindex EAI .cindex i18n -.cindex UTF-8 "mail name handling" +.cindex utf8 "mail name handling" Exim has support for Internationalised mail names. To include this it must be built with SUPPORT_I18N and the libidn library. @@ -39240,6 +39606,7 @@ form of the name. .cindex log protocol .cindex SMTPUTF8 logging +.cindex i18n logging Log lines and Received-by: header lines will acquire a "utf8" prefix on the protocol element, eg. utf8esmtp. @@ -39251,7 +39618,12 @@ ${utf8_localpart_to_alabel:str} ${utf8_localpart_from_alabel:str} .endd -ACLs may use the following modifier: +.cindex utf8 "address downconversion" +.cindex i18n "utf8 address downconversion" +.new +The RCPT ACL +.wen +may use the following modifier: .display control = utf8_downconvert control = utf8_downconvert/ @@ -39295,7 +39667,7 @@ the "headers charset" command (in a filter file) or &%headers_charset%& main configuration option (otherwise), to the modified UTF-7 encoding specified by RFC 2060, -with the following exception: All occurences of +with the following exception: All occurrences of (which has to be a single character) are replaced with periods ("."), and all periods and slashes that are not and are not in the string are BASE64 encoded. @@ -39359,6 +39731,7 @@ expansion must check this, as it will be called for every possible event type. The current list of events is: .display +&`dane:fail after transport `& per connection &`msg:complete after main `& per message &`msg:delivery after transport `& per recipient &`msg:rcpt:host:defer after transport `& per recipient per host @@ -39381,12 +39754,13 @@ The second column in the table above describes whether the event fires before or after the action is associates with. Those which fire before can be used to affect that action (more on this below). -The third column in the table above says what section of the configumration +The third column in the table above says what section of the configuration should define the event action. An additional variable, &$event_data$&, is filled with information varying with the event type: .display +&`dane:fail `& failure reason &`msg:delivery `& smtp confirmation message &`msg:rcpt:host:defer `& error string &`msg:rcpt:defer `& error string @@ -39414,15 +39788,12 @@ The expansion of the event_action option should normally return an empty string. Should it return anything else the following will be forced: .display -&`msg:delivery `& (ignored) -&`msg:host:defer `& (ignored) -&`msg:fail:delivery`& (ignored) &`tcp:connect `& do not connect -&`tcp:close `& (ignored) &`tls:cert `& refuse verification &`smtp:connect `& close connection .endd -No other use is made of the result string. +All other message types ignore the result string, and +no other use is made of it. For a tcp:connect event, if the connection is being made to a proxy then the address and port variables will be that of the proxy and not