X-Git-Url: https://git.exim.org/users/jgh/exim.git/blobdiff_plain/c4b57fddcae8301f324d2626083c13b2c5e60521..36f7a17f69fe27a4c04a4ff98f80f780007db175:/doc/doc-docbook/spec.xfpt?ds=inline diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index f950a4dac..0d6c23907 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -45,14 +45,14 @@ . Update the Copyright year (only) when changing content. . ///////////////////////////////////////////////////////////////////////////// -.set previousversion "4.90" +.set previousversion "4.91" .include ./local_params .set ACL "access control lists (ACLs)" .set I "    " .macro copyyear -2017 +2018 .endmacro . ///////////////////////////////////////////////////////////////////////////// @@ -448,12 +448,9 @@ available in other formats (HTML, PostScript, PDF, and Texinfo). Section .section "FTP and web sites" "SECID2" .cindex "web site" .cindex "FTP site" -The primary site for Exim source distributions is currently the University of -Cambridge's FTP site, whose contents are described in &'Where to find the Exim -distribution'& below. In addition, there is a web site and an FTP site at -&%exim.org%&. These are now also hosted at the University of Cambridge. The -&%exim.org%& site was previously hosted for a number of years by Energis -Squared, formerly Planet Online Ltd, whose support I gratefully acknowledge. +The primary site for Exim source distributions is the &%exim.org%& FTP site, +available over HTTPS, HTTP and FTP. These services, and the &%exim.org%& +website, are hosted at the University of Cambridge. .cindex "wiki" .cindex "FAQ" @@ -462,12 +459,14 @@ differently formatted versions of the documentation. A recent addition to the online information is the Exim wiki (&url(http://wiki.exim.org)), which contains what used to be a separate FAQ, as well as various other examples, tips, and know-how that have been contributed by Exim users. +The wiki site should always redirect to the correct place, which is currently +provided by GitHub, and is open to editing by anyone with a GitHub account. .cindex Bugzilla An Exim Bugzilla exists at &url(https://bugs.exim.org). You can use this to report bugs, and also to add items to the wish list. Please search first to check that you are not duplicating a previous entry. - +Please do not ask for configuration help in the bug-tracker. .section "Mailing lists" "SECID3" @@ -505,26 +504,41 @@ message to the &'exim-dev'& mailing list and have it discussed. .section "Where to find the Exim distribution" "SECTavail" .cindex "FTP site" +.cindex "HTTPS download site" .cindex "distribution" "ftp site" -The master ftp site for the Exim distribution is +.cindex "distribution" "https site" +The master distribution site for the Exim distribution is .display -&*ftp://ftp.exim.org/pub/exim*& +&*https://downloads.exim.org/*& .endd -The file references that follow are relative to the &_exim_& directories at -these sites. There are now quite a number of independent mirror sites around +The service is available over HTTPS, HTTP and FTP. +We encourage people to migrate to HTTPS. + +The content served at &'https://downloads.exim.org/'& is identical to the +content served at &'https://ftp.exim.org/pub/exim'& and +&'ftp://ftp.exim.org/pub/exim'&. + +If accessing via a hostname containing &'ftp'&, then the file references that +follow are relative to the &_exim_& directories at these sites. +If accessing via the hostname &'downloads'& then the subdirectories described +here are top-level directories. + +There are now quite a number of independent mirror sites around the world. Those that I know about are listed in the file called &_Mirrors_&. -Within the &_exim_& directory there are subdirectories called &_exim3_& (for +Within the top exim directory there are subdirectories called &_exim3_& (for previous Exim 3 distributions), &_exim4_& (for the latest Exim 4 distributions), and &_Testing_& for testing versions. In the &_exim4_& subdirectory, the current release can always be found in files called .display +&_exim-n.nn.tar.xz_& &_exim-n.nn.tar.gz_& &_exim-n.nn.tar.bz2_& .endd -where &'n.nn'& is the highest such version number in the directory. The two +where &'n.nn'& is the highest such version number in the directory. The three files contain identical data; the only difference is the type of compression. -The &_.bz2_& file is usually a lot smaller than the &_.gz_& file. +The &_.xz_& file is usually the smallest, while the &_.gz_& file is the +most portable to old systems. .cindex "distribution" "signing details" .cindex "distribution" "public key" @@ -538,17 +552,14 @@ PGP key, a version of which can be found in the release directory in the file &_nigel-pubkey.asc_&. All keys used will be available in public keyserver pools, such as &'pool.sks-keyservers.net'&. -At time of last update, releases were being made by Phil Pennock and signed with -key &'0x403043153903637F'&, although that key is expected to be replaced in 2013. -A trust path from Nigel's key to Phil's can be observed at -&url(https://www.security.spodhuis.org/exim-trustpath). - -Releases have also been authorized to be performed by Todd Lyons who signs with -key &'0xC4F4F94804D29EBA'&. A direct trust path exists between previous RE Phil -Pennock and Todd Lyons through a common associate. +At time of last update, releases were being made by Jeremy Harris and signed +with key &'0xBCE58C8CE41F32DF'&. Other recent keys used for signing are those +of Heiko Schlittermann, &'0x26101B62F69376CE'&, +and of Phil Pennock, &'0x4D1E900E14C1CC04'&. The signatures for the tar bundles are in: .display +&_exim-n.nn.tar.xz.asc_& &_exim-n.nn.tar.gz.asc_& &_exim-n.nn.tar.bz2.asc_& .endd @@ -567,7 +578,7 @@ inside the &_exim4_& directory of the FTP site: &_exim-texinfo-n.nn.tar.gz_& .endd These tar files contain only the &_doc_& directory, not the complete -distribution, and are also available in &_.bz2_& as well as &_.gz_& forms. +distribution, and are also available in &_.bz2_& and &_.xz_& forms. .section "Limitations" "SECID6" @@ -3162,10 +3173,8 @@ 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%&" @@ -3838,7 +3847,7 @@ alternate queue is used, named by the following argument. .vitem &%-MCK%& .oindex "&%-MCK%&" This option is not intended for use by external callers. It is used internally -by Exim in conjunction with the &%-MC%& option. It signifies that an +by Exim in conjunction with the &%-MC%& option. It signifies that a remote host supports the ESMTP &_CHUNKING_& extension. .vitem &%-MCP%& @@ -7839,6 +7848,17 @@ ${lookup redis{set keyname ${quote_redis:objvalue plus}}} ${lookup redis{get keyname}} .endd +As of release 4.91, "lightweight" support for Redis Cluster is available. +Requires &%redis_servers%& list to contain all the servers in the cluster, all +of which must be reachable from the running exim instance. If the cluster has +master/slave replication, the list must contain all the master and slave +servers. + +When the Redis Cluster returns a "MOVED" response to a query, Exim does not +immediately follow the redirection but treats the response as a DEFER, moving on +to the next server in the &%redis_servers%& list until the correct server is +reached. + .ecindex IIDfidalo1 .ecindex IIDfidalo2 @@ -9137,16 +9157,16 @@ the expansion result is an empty string. If the ACL returns defer the result is a forced-fail. Otherwise the expansion fails. -.new .vitem "&*${authresults{*&<&'authserv-id'&>&*}}*&" .cindex authentication "results header" .cindex headers "authentication-results:" +.cindex authentication "expansion item" 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: +will be a domain name identifying the system performing the authentications. +Methods that might be present in the result include: .code none iprev @@ -9159,7 +9179,7 @@ Example use (as an ACL modifier): .code add_header = :at_start:${authresults {$primary_hostname}} .endd -.wen +This is safe even if no authentication results are available. .vitem "&*${certextract{*&<&'field'&>&*}{*&<&'certificate'&>&*}&&& @@ -9414,11 +9434,14 @@ letters appear. For example: &*$h_*&<&'header&~name'&>&*:*&" &&& "&*$bheader_*&<&'header&~name'&>&*:*&&~or&~&&& &*$bh_*&<&'header&~name'&>&*:*&" &&& + "&*$lheader_*&<&'header&~name'&>&*:*&&~or&~&&& + &*$lh_*&<&'header&~name'&>&*:*&" "&*$rheader_*&<&'header&~name'&>&*:*&&~or&~&&& &*$rh_*&<&'header&~name'&>&*:*&" .cindex "expansion" "header insertion" .vindex "&$header_$&" .vindex "&$bheader_$&" +.vindex "&$lheader_$&" .vindex "&$rheader_$&" .cindex "header lines" "in expansion strings" .cindex "header lines" "character sets" @@ -9431,7 +9454,7 @@ The newline that terminates a header line is not included in the expansion, but internal newlines (caused by splitting the header line over several physical lines) may be present. -The difference between &%rheader%&, &%bheader%&, and &%header%& is in the way +The difference between the four pairs of expansions is in the way the data in the header line is interpreted. .ilist @@ -9439,6 +9462,15 @@ the data in the header line is interpreted. &%rheader%& gives the original &"raw"& content of the header line, with no processing at all, and without the removal of leading and trailing white space. +.next +.cindex "list" "of header lines" +&%lheader%& gives a colon-separated list, one element per header when there +are multiple headers with a given name. +Any embedded colon characters within an element are doubled, so normal Exim +list-processing facilities can be used. +The terminating newline of each element is removed; in other respects +the content is &"raw"&. + .next .cindex "base64 encoding" "in header lines" &%bheader%& removes leading and trailing white space, and then decodes base64 @@ -10675,10 +10707,8 @@ with 256 being the default. The &%sha3%& expansion item is only supported if Exim has been 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 &*${stat:*&<&'string'&>&*}*& @@ -11580,10 +11610,13 @@ preserve some of the authentication information in the variable user/password authenticator configuration might preserve the user name for use in the routers. Note that this is not the same information that is saved in &$sender_host_authenticated$&. + When a message is submitted locally (that is, not over a TCP connection) the value of &$authenticated_id$& is normally the login name of the calling process. However, a trusted user can override this by means of the &%-oMai%& command line option. +This second case also sets up inforamtion used by the +&$authresults$& expansion item. .vitem &$authenticated_fail_id$& .cindex "authentication" "fail" "id" @@ -11923,6 +11956,11 @@ lookup succeeds, but there is a lookup problem such as a timeout when checking the result, the name is not accepted, and &$host_lookup_deferred$& is set to &"1"&. See also &$sender_host_name$&. +.cindex authentication "expansion item" +Performing these checks sets up information used by the +&$authresults$& expansion item. + + .vitem &$host_lookup_failed$& .vindex "&$host_lookup_failed$&" See &$host_lookup_deferred$&. @@ -12874,14 +12912,13 @@ A number of variables whose names start with &$spam$& are available when Exim is compiled with the content-scanning extension. For details, see section &<>&. -.new .vitem &$spf_header_comment$& &&& &$spf_received$& &&& &$spf_result$& &&& + &$spf_result_guessed$& &&& &$spf_smtp_comment$& These variables are only available if Exim is built with SPF support. For details see section &<>&. -.wen .vitem &$spool_directory$& .vindex "&$spool_directory$&" @@ -12944,7 +12981,8 @@ It is only useful as the argument of a &%certextract%& expansion item, &%md5%&, &%sha1%& or &%sha256%& operator, or a &%def%& condition. -&*Note*&: Under current versions of OpenSSL, when a list of more than one +&*Note*&: Under versions of OpenSSL preceding 1.1.1, +when a list of more than one file is used for &%tls_certificate%&, this variable is not reliable. .vitem &$tls_in_peercert$& @@ -15056,7 +15094,7 @@ server. This reduces security slightly, but improves interworking with older implementations of TLS. -option gnutls_allow_auto_pkcs11 main boolean unset +.option gnutls_allow_auto_pkcs11 main boolean unset This option will let GnuTLS (2.12.0 or later) autoload PKCS11 modules with the p11-kit configuration files in &_/etc/pkcs11/modules/_&. @@ -16878,11 +16916,9 @@ See section &<>& for more details. -.new .option spf_guess main string "v=spf1 a/24 mx/24 ptr ?all" This option is available when Exim is compiled with SPF support. See section &<>& for more details. -.wen @@ -16938,10 +16974,10 @@ tests of Exim without using the standard spool. .option spool_wireformat main boolean false .cindex "spool directory" "file formats" -If this option is set, Exim may for some messages use an alternate format +If this option is set, Exim may for some messages use an alternative format for data-files in the spool which matches the wire format. Doing this permits more efficient message reception and transmission. -Currently it is only done for messages received using the EMSTP CHUNKING +Currently it is only done for messages received using the ESMTP CHUNKING option. The following variables will not have useful values: @@ -16954,7 +16990,7 @@ $body_zerocount Users of the local_scan() API (see &<>&), and any external programs which are passed a reference to a message data file (except via the &"regex"&, &"malware"& or &"spam"&) ACL conditions) -will need to be aware of the potential different format. +will need to be aware of the different formats potentially available. Using any of the ACL conditions noted will negate the reception benefit (as a Unix-mbox-format file is constructed for them). @@ -17184,7 +17220,8 @@ option in the relevant &(smtp)& transport. &*Note*&: If you use filenames based on IP addresses, change the list separator in the usual way to avoid confusion under IPv6. -&*Note*&: Under current versions of OpenSSL, when a list of more than one +&*Note*&: Under versions of OpenSSL preceding 1.1.1, +when a list of more than one file is used, the &$tls_in_ourcert$& variable is unreliable. &*Note*&: OCSP stapling is not usable under OpenSSL @@ -17204,13 +17241,11 @@ generated for every connection. This option specifies a certificate revocation list. The expanded value must be the name of a file that contains CRLs in PEM format. -.new Under OpenSSL the option can specify a directory with CRL files. &*Note:*& Under OpenSSL the option must, if given, supply a CRL for each signing element of the certificate chain (i.e. all but the leaf). For the file variant this can be multiple PEM blocks in the one file. -.wen See &<>& for discussion of when this option might be re-expanded. @@ -17337,18 +17372,16 @@ Certificate Authority. Usable for GnuTLS 3.4.4 or 3.3.17 or OpenSSL 1.1.0 (or later). -.new For GnuTLS 3.5.6 or later the expanded value of this option can be a list of files, to match a list given for the &%tls_certificate%& option. The ordering of the two lists must match. -.wen .option tls_on_connect_ports main "string list" unset .cindex SSMTP .cindex SMTPS This option specifies a list of incoming SSMTP (aka SMTPS) ports that should -operate the obsolete SSMTP (SMTPS) protocol, where a TLS session is immediately +operate the SSMTP (SMTPS) protocol, where a TLS session is immediately set up without waiting for the client to issue a STARTTLS command. For further details, see section &<>&. @@ -18804,9 +18837,7 @@ 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, -.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. @@ -18939,7 +18970,6 @@ 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" @@ -18955,7 +18985,6 @@ 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" @@ -19582,12 +19611,10 @@ 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: @@ -23913,6 +23940,22 @@ For testing purposes, this value can be overridden by the &%-oB%& command line option. +.option dane_require_tls_ciphers smtp string&!! unset +.cindex "TLS" "requiring specific ciphers for DANE" +.cindex "cipher" "requiring specific" +.cindex DANE "TLS ciphers" +This option may be used to override &%tls_require_ciphers%& for connections +where DANE has been determined to be in effect. +If not set, then &%tls_require_ciphers%& will be used. +Normal SMTP delivery is not able to make strong demands of TLS cipher +configuration, because delivery will fall back to plaintext. Once DANE has +been determined to be in effect, there is no plaintext fallback and making the +TLS cipherlist configuration stronger will increase security, rather than +counter-intuitively decreasing it. +If the option expands to be empty or is forced to fail, then it will +be treated as unset and &%tls_require_ciphers%& will be used instead. + + .option data_timeout smtp time 5m This sets a timeout for the transmission of each block in the data portion of the message. As a result, the overall timeout for a message depends on the size @@ -24234,7 +24277,6 @@ 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" @@ -24243,7 +24285,6 @@ 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" @@ -24274,7 +24315,6 @@ 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" @@ -24284,7 +24324,6 @@ 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" @@ -26091,6 +26130,10 @@ public name) of the authenticator driver that successfully authenticated the client from which the message was received. This variable is empty if there was no successful authentication. +.cindex authentication "expansion item" +Successful authentication sets up information used by the +&$authresults$& expansion item. + @@ -26183,8 +26226,8 @@ deliver the message unauthenticated. Note that the hostlist test for whether to do authentication can be confused if name-IP lookups change between the time the peer is decided -on and the transport running. For example, with a manualroute -router given a host name, and DNS "round-robin" use by that name: if +upon and the time that the transport runs. For example, with a manualroute +router given a host name, and with DNS "round-robin" used by that name: if the local resolver cache times out between the router and the transport running, the transport may get an IP for the name for its authentication check which does not match the connection peer IP. @@ -27177,7 +27220,7 @@ 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. +by them 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 @@ -27188,8 +27231,8 @@ 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. +In practice, a number of mail-clients have only ever 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%& @@ -28042,7 +28085,6 @@ 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 @@ -28068,8 +28110,7 @@ that DNS lookups they do for the server have not been tampered with. The domain 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 +3) offer a server certificate, or certificate chain, in TLS connections which is is anchored by one of the TLSA 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 @@ -28088,6 +28129,9 @@ the entire certificate chain from CA to server-certificate. If a public CA is u 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. +Another approach which should be seriously considered is to use DANE with a certificate +from a public CA, because of another technology, "MTA-STS", described below. + 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) @@ -28124,8 +28168,9 @@ This modification of hosts_request_ocsp is only done if it has the default value 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. +For client-side DANE there are three new smtp transport options, &%hosts_try_dane%&, &%hosts_require_dane%& +and &%dane_require_tls_ciphers%&. +The require 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. @@ -28134,6 +28179,14 @@ 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 usable, then the TLS cipher list configuration +prefers to use the option &%dane_require_tls_ciphers%& and falls +back to &%tls_require_ciphers%& only if that is unset. +This lets you configure "decent crypto" for DANE and "better than nothing +crypto" as the default. Note though that while GnuTLS lets the string control +which versions of TLS/SSL will be negotiated, OpenSSL does not and you're +limited to ciphersuite constraints. + If DANE is requested and useable (see above) the following transport options are ignored: .code hosts_require_tls @@ -28165,7 +28218,28 @@ 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 + +DANE is specified in published RFCs and decouples certificate authority trust +selection from a "race to the bottom" of "you must trust everything for mail +to get through". There is an alternative technology called MTA-STS, which +instead publishes MX trust anchor information on an HTTPS website. At the +time this text was last updated, MTA-STS was still a draft, not yet an RFC. +Exim has no support for MTA-STS as a client, but Exim mail server operators +can choose to publish information describing their TLS configuration using +MTA-STS to let those clients who do use that protocol derive trust +information. + +The MTA-STS design requires a certificate from a public Certificate Authority +which is recognized by clients sending to you. That selection is outside your +control. + +The most interoperable course of action is probably to use +&url(https://letsencrypt.org/,Let's Encrypt), with automated certificate +renewal; to publish the anchor information in DNSSEC-secured DNS via TLSA +records for DANE clients (such as Exim and Postfix) and to publish anchor +information for MTA-STS as well. This is what is done for the &'exim.org'& +domain itself (with caveats around occasionally broken MTA-STS because of +incompatible specification changes prior to reaching RFC status). @@ -29379,7 +29453,7 @@ and cannot depend on content of received headers. Note also that headers cannot be modified by any of the post-data ACLs (DATA, MIME and DKIM). Headers may be modified by routers (subject to the above) and transports. -The Received-By: header is generated as soon as the body reception starts, +The &'Received-By:'& header is generated as soon as the body reception starts, rather than the traditional time after the full message is received; this will affect the timestamp. @@ -30678,7 +30752,7 @@ restrictions, to get the TXT record. As a byproduct of this, there is also a check that the IP being tested is indeed on the first list. The first domain is the one that is put in &$dnslist_domain$&. For example: .code -reject message = \ +deny message = \ rejected because $sender_host_address is blacklisted \ at $dnslist_domain\n$dnslist_text dnslists = \ @@ -30696,7 +30770,7 @@ If you are interested in more than one merged list, the same list must be given several times, but because the results of the DNS lookups are cached, the DNS calls themselves are not repeated. For example: .code -reject dnslists = \ +deny dnslists = \ http.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.2 : \ socks.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.3 : \ misc.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.4 : \ @@ -30907,13 +30981,15 @@ rest of the ACL. The &%leaky%& (default) option means that the client's recorded rate is not updated if it is above the limit. The effect of this is that Exim measures the -client's average rate of successfully sent email, which cannot be greater than -the maximum allowed. If the client is over the limit it may suffer some -counter-measures (as specified in the ACL), but it will still be able to send -email at the configured maximum rate, whatever the rate of its attempts. This +client's average rate of successfully sent email, +.new +up to the given limit. +This is appropriate if the countermeasure when the condition is true +consists of refusing the message, and is generally the better choice if you have clients that retry automatically. -For example, it does not prevent a sender with an over-aggressive retry rate -from getting any email through. +If the action when true is anything more complex then this option is +likely not what is wanted. +.wen The &%strict%& option means that the client's recorded rate is always updated. The effect of this is that Exim measures the client's average rate @@ -31798,27 +31874,34 @@ If the value of &%av_scanner%& starts with a dollar character, it is expanded before use. The usual list-parsing of the content (see &<>&) applies. The following scanner types are supported in this release, -.new though individual ones can be included or not at build time: -.wen .vlist .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. The host may be a name or an IP address; the port is either a single number or a pair of numbers with a dash between. -Any further options are given, on separate lines, -to the daemon as options before the main scan command. +A list of options may follow. These options are interpreted on the +Exim's side of the malware scanner, or are given on separate lines to +the daemon as options before the main scan command. + +.cindex &`pass_unscanned`& "avast" +If &`pass_unscanned`& +is set, any files the Avast scanner can't scan (e.g. +decompression bombs, or invalid archives) are considered clean. Use with +care. + For example: .code av_scanner = avast:/var/run/avast/scan.sock:FLAGS -fullfiles:SENSITIVITY -pup +av_scanner = avast:/var/run/avast/scan.sock:pass_unscanned:FLAGS -fullfiles:SENSITIVITY -pup av_scanner = avast:192.168.2.22 5036 .endd If you omit the argument, the default path @@ -31835,6 +31918,9 @@ $ socat UNIX:/var/run/avast/scan.sock STDIO: PACK .endd +If the scanner returns a temporary failure (e.g. license issues, or +permission problems), the message is deferred and a paniclog entry is +written. The usual &`defer_ok`& option is available. .vitem &%aveserver%& .cindex "virus scanners" "Kaspersky" @@ -31885,7 +31971,7 @@ av_scanner = clamd:192.0.2.3 1234 : 192.0.2.4 1234 If the value of av_scanner points to a UNIX socket file or contains the &`local`& option, then the ClamAV interface will pass a filename containing the data -to be scanned, which will should normally result in less I/O happening and be +to be scanned, which should normally result in less I/O happening and be more efficient. Normally in the TCP case, the data is streamed to ClamAV as Exim does not assume that there is a common filesystem with the remote host. @@ -31967,7 +32053,7 @@ For example: .code av_scanner = f-protd:localhost 10200-10204 .endd -If you omit the argument, the default values show above are used. +If you omit the argument, the default values shown above are used. .vitem &%f-prot6d%& .cindex "virus scanners" "f-prot6d" @@ -32664,10 +32750,15 @@ code. The incident is logged on the main and reject logs. .section "Building Exim to use a local scan function" "SECID207" .cindex "&[local_scan()]& function" "building Exim to use" To make use of the local scan function feature, you must tell Exim where your -function is before building Exim, by setting LOCAL_SCAN_SOURCE in your +function is before building Exim, by setting +.new +both HAVE_LOCAL_SCAN and +.wen +LOCAL_SCAN_SOURCE in your &_Local/Makefile_&. A recommended place to put it is in the &_Local_& directory, so you might set .code +HAVE_LOCAL_SCAN=yes LOCAL_SCAN_SOURCE=Local/local_scan.c .endd for example. The function must be called &[local_scan()]&. It is called by @@ -36379,11 +36470,9 @@ A delivery set up by a router configured with failed. The delivery was discarded. .endlist olist .next -.new .cindex DKIM "log line" &'DKIM: d='&&~&~Verbose results of a DKIM verification attempt, if enabled for logging and the message has a DKIM signature header. -.wen .endlist ilist @@ -36429,6 +36518,7 @@ selection marked by asterisks: &` queue_time_overall `& time on queue for whole message &` pid `& Exim process id &` proxy `& proxy address on <= and => lines +&` receive_time `& time taken to receive message &` received_recipients `& recipients on <= lines &` received_sender `& sender on <= lines &`*rejected_header `& header contents on reject log @@ -36519,7 +36609,6 @@ precision, eg. &`DT=0.304s`&. &%delivery_size%&: For each delivery, the size of message delivered is added to the &"=>"& line, tagged with S=. .next -.new .cindex log "DKIM verification" .cindex DKIM "verification logging" &%dkim%&: For message acceptance log lines, when an DKIM signature in the header @@ -36528,7 +36617,6 @@ verifies successfully a tag of DKIM is added, with one of the verified domains. .cindex log "DKIM verification" .cindex DKIM "verification logging" &%dkim_verbose%&: A log entry is written for each attempted DKIM verification. -.wen .next .cindex "log" "dnslist defer" .cindex "DNS list" "logging defer" @@ -36650,14 +36738,12 @@ 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 @@ -36815,10 +36901,8 @@ unchanged, or whether they should be rendered as escape sequences. &%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 -.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" @@ -38791,11 +38875,9 @@ 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 6376. -.new As DKIM relies on the message being unchanged in transit, messages handled by a mailing-list (which traditionally adds to the message) will not match any original DKIM signature. -.wen DKIM support is compiled into Exim by default if TLS support is present. It can be disabled by setting DISABLE_DKIM=yes in &_Local/Makefile_&. @@ -38816,7 +38898,6 @@ 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 (in the <= line) purposes. @@ -38830,7 +38911,6 @@ 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 @@ -38842,7 +38922,6 @@ 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 @@ -38857,7 +38936,6 @@ 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. @@ -38886,10 +38964,9 @@ You can use the &%$dkim_domain%& and The result can either .ilist 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 +with GnuTLS 3.6.0 or OpenSSL 1.1.1 or later, +be a valid Ed25519 private key (same format as above) .next start with a slash, in which case it is treated as a file that contains the private key @@ -38899,7 +38976,21 @@ be signed. This case will not result in an error, even if &%dkim_strict%& is set. .endlist -.new +To generate keys under OpenSSL: +.code +openssl genrsa -out dkim_rsa.private 2048 +openssl rsa -in dkim_rsa.private -out /dev/stdout -pubout -outform PEM +.endd +Take the base-64 lines from the output of the second command, concatenated, +for the DNS TXT record. +See section 3.6 of RFC6376 for the record specification. + +Under GnuTLS: +.code +certtool --generate-privkey --rsa --bits=2048 --password='' -8 --outfile=dkim_rsa.private +certtool --load-privkey=dkim_rsa.private --pubkey-info +.endd + Note that RFC 8301 says: .code Signers MUST use RSA keys of at least 1024 bits for all keys. @@ -38914,18 +39005,38 @@ As they are a recent development, users should consider dual-signing for some transition period. The "_CRYPTO_SIGN_ED25519" macro will be defined if support is present for EC keys. -.wen + +OpenSSL 1.1.1 and GnuTLS 3.6.0 can create Ed25519 private keys: +.code +openssl genpkey -algorithm ed25519 -out dkim_ed25519.private +certtool --generate-privkey --key-type=ed25519 --outfile=dkim_ed25519.private +.endd + +To produce the required public key value for a DNS record: +.code +openssl pkey -outform DER -pubout -in dkim_ed25519.private | tail -c +13 | base64 +certtool --load_privkey=dkim_ed25519.private --pubkey_info --outder | tail -c +13 | base64 +.endd + +Note that the format +of Ed25519 keys in DNS has not yet been decided; this release supports +both of the leading candidates at this time, a future release will +probably drop support for whichever proposal loses. .option dkim_hash smtp string&!! sha256 -Can be set alternatively to &"sha1"& to use an alternate hash -method. +Can be set to any one of the supported hash methods, which are: +.ilist +&`sha1`& &-- should not be used, is old and insecure +.next +&`sha256`& &-- the default +.next +&`sha512`& &-- possibly more secure but less well supported +.endlist -.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 @@ -38938,7 +39049,7 @@ tag value. Note that Exim does not check the value. This option sets the canonicalization method used when signing a message. The DKIM RFC currently supports two methods: "simple" and "relaxed". The option defaults to "relaxed" when unset. Note: the current implementation -only supports using the same canonicalization method for both headers and body. +only supports signing with the same canonicalization method for both headers and body. .option dkim_strict smtp string&!! unset This option defines how Exim behaves when signing a message that @@ -38972,15 +39083,25 @@ name will be appended. .section "Verifying DKIM signatures in incoming mail" "SECDKIMVFY" .cindex "DKIM" "verification" -Verification of DKIM signatures in SMTP incoming email is implemented via the -&%acl_smtp_dkim%& ACL. By default, this ACL is called once for each +.new +Verification of DKIM signatures in SMTP incoming email is done for all +messages for which an ACL control &%dkim_disable_verify%& has not been set. +.cindex authentication "expansion item" +Performing verification sets up information used by the +&$authresults$& expansion item. +.wen + +.new The results of that verification are then made available to the +&%acl_smtp_dkim%& ACL, &new(which can examine and modify them). +By default, this ACL is called once for each syntactically(!) correct signature in the incoming message. A missing ACL definition defaults to accept. If any ACL call does not accept, the message is not accepted. If a cutthrough delivery was in progress for the message, that is summarily dropped (having wasted the transmission effort). -To evaluate the signature in the ACL a large number of expansion variables +To evaluate the &new(verification result) in the ACL +a large number of expansion variables containing the signature status and its details are set up during the runtime of the ACL. @@ -39049,13 +39170,13 @@ 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_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 or key too short + warn condition = ${if eq {$dkim_verify_status}{pass}} + condition = ${if eq {${length_3:$dkim_algo}}{rsa}} + condition = ${if or {{eq {$dkim_algo}{rsa-sha1}} \ + {< {$dkim_key_length}{1024}}}} + logwrite = NOTE: forcing DKIM verify fail (was pass) + set dkim_verify_status = fail + set dkim_verify_reason = hash too weak or key too short .endd After all the DKIM ACL runs have completed, the value becomes a @@ -39098,13 +39219,11 @@ The key record selector string. .vitem &%$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'. +If running under GnuTLS 3.6.0 or OpenSSL 1.1.1 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. @@ -39115,7 +39234,6 @@ algorithms (currently, rsa-sha1) have permanently failed evaluation 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 &%$dkim_canon_body%& The body canonicalization method. One of 'relaxed' or 'simple'. @@ -39144,9 +39262,7 @@ UNIX timestamp reflecting the date and time when the signer wants the signature to be treated as "expired". When this was not specified by the signer, "9999999999999" is returned. This makes it possible to do useful integer size comparisons against this value. -.new Note that Exim does not check this value. -.wen .vitem &%$dkim_headernames%& A colon-separated list of names of headers included in the signature. @@ -39171,7 +39287,6 @@ Notes from the key record (tag n=). .vitem &%$dkim_key_length%& Number of bits in the key. -.new Note that RFC 8301 says: .code Verifiers MUST NOT consider signatures using RSA keys of @@ -39181,7 +39296,6 @@ less than 1024 bits as valid signatures. To enforce this you must have a DKIM ACL which checks this variable and overwrites the &$dkim_verify_status$& variable as discussed above. As EC keys are much smaller, the check should only do this for RSA keys. -.wen .endlist @@ -39225,7 +39339,6 @@ for more information of what they mean. -.new .section "SPF (Sender Policy Framework)" SECSPF .cindex SPF verification @@ -39239,10 +39352,14 @@ This includes retransmissions done by traditional forwarders. SPF verification support is built into Exim if SUPPORT_SPF=yes is set in &_Local/Makefile_&. The support uses the &_libspf2_& library &url(http://www.libspf2.org/). -There is no Exim involvement on the trasmission of messages; publishing certain -DNS records is all that is required. +There is no Exim involvement in the transmission of messages; +publishing certain DNS records is all that is required. For verification, an ACL condition and an expansion lookup are provided. +.cindex authentication "expansion item" +Performing verification sets up information used by the +&$authresults$& expansion item. + .cindex SPF "ACL condition" .cindex ACL "spf condition" @@ -39272,18 +39389,11 @@ its domain as well. This should be treated like "none". .vitem &%permerror%& This indicates a syntax error in the SPF record of the queried domain. -You may deny messages when this occurs. (Changed in 4.83) +You may deny messages when this occurs. .vitem &%temperror%& This indicates a temporary error during all processing, including Exim's SPF processing. You may defer messages when this occurs. -(Changed in 4.83) - -.vitem &%err_temp%& -Same as permerror, deprecated in 4.83, will be removed in a future release. - -.vitem &%err_perm%& -Same as temperror, deprecated in 4.83, will be removed in a future release. .endlist You can prefix each string with an exclamation mark to invert @@ -39331,6 +39441,11 @@ variables: one of pass, fail, softfail, none, neutral, permerror or temperror. +.vitem &$spf_result_guessed$& +.vindex &$spf_result_guessed$& + This boolean is true only if a best-guess operation was used + and required in order to obtain a result. + .vitem &$spf_smtp_comment$& .vindex &$spf_smtp_comment$& This contains a string that can be used in a SMTP response @@ -39385,13 +39500,11 @@ address as the key and an IP address as the database: ${lookup {username@domain} spf {ip.ip.ip.ip}} .endd -The lookup will return the same result strings as they can appear in +The lookup will return the same result strings as can appear in &$spf_result$& (pass,fail,softfail,neutral,none,err_perm,err_temp). Currently, only IPv4 addresses are supported. -. wen-for SPF section -.wen . //////////////////////////////////////////////////////////////////////////// @@ -39607,9 +39720,7 @@ ${utf8_localpart_from_alabel:str} .cindex utf8 "address downconversion" .cindex i18n "utf8 address downconversion" -.new The RCPT ACL -.wen may use the following modifier: .display control = utf8_downconvert