X-Git-Url: https://git.exim.org/users/jgh/exim.git/blobdiff_plain/dbbf21a75d225871cb7a44878ece42c5d79a1a2c..9300a61f79604940f3b0c6fbc4b72f1a3c882caf:/doc/doc-docbook/spec.xfpt diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index aa3996505..51c4e0160 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -6109,6 +6109,9 @@ dnslookup: domains = ! +local_domains transport = remote_smtp ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8 +.ifdef _HAVE_DNSSEC + dnssec_request_domains = * +.endif no_more .endd The &%domains%& option behaves as per smarthost, above. @@ -6260,7 +6263,6 @@ remote_smtp: driver = smtp message_size_limit = ${if > {$max_received_linelength}{998} {1}{0}} .ifdef _HAVE_DANE - dnssec_request_domains = * hosts_try_dane = * .endif .ifdef _HAVE_PRDR @@ -6271,7 +6273,7 @@ This transport is used for delivering messages over SMTP connections. The list of remote hosts comes from the router. The &%message_size_limit%& usage is a hack to avoid sending on messages with over-long lines. The built-in macro _HAVE_DANE guards configuration -to try to use DNSSEC for all queries and to use DANE for delivery; +to use DANE for delivery; see section &<>& for more details. The &%hosts_try_prdr%& option enables an efficiency SMTP option. It is @@ -14347,7 +14349,9 @@ listed in more than one group. See also the &'Policy controls'& section above. .table2 -.row &%dkim_verify_signers%& "DKIM domain for which DKIM ACL is run" +.row &%dkim_verify_hashes%& "DKIM hash methods accepted for signatures" +.row &%dkim_verify_keytypes%& "DKIM key types accepted for signatures" +.row &%dkim_verify_signers%& "DKIM domains for which DKIM ACL is run" .row &%host_lookup%& "host name looked up for these hosts" .row &%host_lookup_order%& "order of DNS and local name lookups" .row &%recipient_unqualified_hosts%& "may send unqualified recipients" @@ -15092,6 +15096,27 @@ etc. are ignored. If IP literals are enabled, the &(ipliteral)& router declines to handle IPv6 literal addresses. +.new +.option dkim_verify_hashes main "string list" "sha256 : sha512 : sha1" +.cindex DKIM "selecting signature algorithms" +This option gives a list of hash types which are acceptable in signatures, +and an order of processing. +Signatures with algorithms not in the list will be ignored. + +Note that the presence of sha1 violates RFC 8301. +Signatures using the rsa-sha1 are however (as of writing) still common. +The default inclusion of sha1 may be dropped in a future release. + +.option dkim_verify_keytypes main "string list" "ed25519 : rsa" +This option gives a list of key types which are acceptable in signatures, +and an order of processing. +Signatures with algorithms not in the list will be ignored. + +.option dkim_verify_minimal main boolean false +If set to true, verification of signatures will terminate after the +first success. +.wen + .option dkim_verify_signers main "domain list&!!" $dkim_signers .cindex DKIM "controlling calls to the ACL" This option gives a list of DKIM domains for which the DKIM ACL is run. @@ -16018,6 +16043,10 @@ when Exim is entered, so it can, for example, contain a reference to the host name. If no specific path is set for the log files at compile or runtime, or if the option is unset at runtime (i.e. &`log_file_path = `&) they are written in a sub-directory called &_log_& in Exim's spool directory. +.new +A path must start with a slash. +To send to syslog, use the word &"syslog"&. +.wen Chapter &<>& contains further details about Exim's logging, and section &<>& describes how the contents of &%log_file_path%& are used. If this string is fixed at your installation (contains no expansion @@ -16875,11 +16904,11 @@ it qualifies them only if the message came from a host that matches &%sender_unqualified_hosts%&, or if the message was submitted locally (not using TCP/IP), and the &%-bnq%& option was not set. -.option set_environment main "string list" empty +.option add_environment main "string list" empty .cindex "environment" -This option allows to set individual environment variables that the +This option allows to add individual environment variables that the currently linked libraries and programs in child processes use. The -default list is empty, +default list is empty. .option slow_lookup_log main integer 0 @@ -17621,8 +17650,8 @@ is not required the &%tls_advertise_hosts%& option should be set empty. .cindex "TLS" "server certificate; location of" .cindex "certificate" "server, location of" The value of this option is expanded, and must then be a list of absolute paths to -files which contains the server's certificates. Commonly only one file is -needed. +files which contain the server's certificates (in PEM format). +Commonly only one file is needed. The server's private key is also assumed to be in this file if &%tls_privatekey%& is unset. See chapter &<>& for further details. @@ -17791,6 +17820,7 @@ 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. +The file(s) should be in DER format .option tls_on_connect_ports main "string list" unset .cindex SSMTP @@ -18886,7 +18916,7 @@ This option controls whether the local part is used to form the key for retry hints for addresses that suffer temporary errors while being handled by this .new router. The default value is true for any router that has any of -&%check_local_user%&, +&%check_local_user%&, &%local_parts%&, &%condition%&, &%local_part_prefix%&, @@ -22836,6 +22866,15 @@ sometimes add other information onto the ends of message filenames. Section &<>& contains further information. +.new +This option should not be used when other message-handling software +may duplicate messages by making hardlinks to the files. When that is done Exim +will count the message size once for each filename, in contrast with the actual +disk usage. When the option is not set, calculating total usage requires +a system-call per file to get the size; the number of links is then available also +as is used to adjust the effective size. +.wen + .option quota_warn_message appendfile string&!! "see below" See below for the use of this option. If it is not set when @@ -24430,15 +24469,23 @@ of the message. Its value must not be zero. See also &%final_timeout%&. .option dkim_canon smtp string&!! unset +DKIM signing option. For details see section &<>&. .option dkim_domain smtp string list&!! unset +DKIM signing option. For details see section &<>&. .option dkim_hash smtp string&!! sha256 +DKIM signing option. For details see section &<>&. .option dkim_identity smtp string&!! unset +DKIM signing option. For details see section &<>&. .option dkim_private_key smtp string&!! unset +DKIM signing option. For details see section &<>&. .option dkim_selector smtp string&!! unset +DKIM signing option. For details see section &<>&. .option dkim_strict smtp string&!! unset +DKIM signing option. For details see section &<>&. .option dkim_sign_headers smtp string&!! "per RFC" +DKIM signing option. For details see section &<>&. .option dkim_timestamps smtp string&!! unset -DKIM signing options. For details see section &<>&. +DKIM signing option. For details see section &<>&. .option delay_after_cutoff smtp boolean true @@ -24486,8 +24533,9 @@ details. .cindex "security" "MX lookup" .cindex "DNS" "DNSSEC" DNS lookups for domains matching &%dnssec_request_domains%& will be done with -the dnssec request bit set. -This applies to all of the SRV, MX, AAAA, A lookup sequence. +the dnssec request bit set. Setting this transport option is only useful if the +transport overrides or sets the host names. See the &%dnssec_request_domains%& +router option. @@ -24497,9 +24545,9 @@ This applies to all of the SRV, MX, AAAA, A lookup sequence. .cindex "security" "MX lookup" .cindex "DNS" "DNSSEC" DNS lookups for domains matching &%dnssec_require_domains%& will be done with -the dnssec request bit set. Any returns not having the Authenticated Data bit -(AD bit) set will be ignored and logged as a host-lookup failure. -This applies to all of the SRV, MX, AAAA, A lookup sequence. +the dnssec request bit set. Setting this transport option is only +useful if the transport overrides or sets the host names. See the +&%dnssec_require_domains%& router option. @@ -24778,7 +24826,8 @@ TLS session for any host that matches this list. .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. +and that a DANE-verified TLS connection is made. See +the &%dnssec_request_domains%& router and transport options. There will be no fallback to in-clear communication. See section &<>&. @@ -24814,11 +24863,11 @@ BDAT will not be used in conjunction with a transport filter. .option hosts_try_dane smtp "host list&!!" * .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. +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. See +the &%dnssec_request_domains%& router and transport options. +There will be no fallback to in-clear communication. See section &<>&. .option hosts_try_fastopen smtp "host list&!!" * @@ -28631,7 +28680,7 @@ Great care should be taken to deal with matters of case, various injection attacks in the string (&`../`& or SQL), and ensuring that a valid filename can always be referenced; it is important to remember that &$tls_in_sni$& is arbitrary unverified data provided prior to authentication. -Further, the initial certificate is loaded before SNI is arrived, so +Further, the initial certificate is loaded before SNI has arrived, so an expansion for &%tls_certificate%& must have a default which is used when &$tls_in_sni$& is empty. @@ -28826,7 +28875,12 @@ Support for client-side operation of DANE can be included at compile time by def 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). +A TLSA record consist of 4 fields, the "Certificate Usage", the +"Selector", the "Matching type", and the "Certificate Association Data". +For a detailed description of the TLSA record see +&url(https://tools.ietf.org/html/rfc7671#page-5,RFC 7671). + +The TLSA record for the server may have "Certificate Usage" (1st) field of DANE-TA(2) or DANE-EE(3). These are the "Trust Anchor" and "End Entity" variants. The latter specifies the End Entity directly, i.e. the certificate involved is that of the server (and if only DANE-EE is used then it should be the sole one transmitted during the TLS handshake); @@ -28867,19 +28921,29 @@ If you're not already using a private CA, or it doesn't meet these requirements, then we encourage you to avoid all these issues and use a public CA such as &url(https://letsencrypt.org/,Let's Encrypt) instead. -The TLSA record should have a Selector field of SPKI(1) and a Matching Type field of SHA2-512(2). +The TLSA record should have a "Selector" (2nd) field of SPKI(1) and +a "Matching Type" (3rd) 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 +For the "Certificate Authority Data" (4th) field, commands like .code - openssl x509 -in -pubkey -noout /dev/null \ | openssl sha512 \ | awk '{print $2}' .endd -are workable for 4th-field hashes. +are workable to create a hash of the certificate's public key. + +An example TLSA record for DANE-EE(3), SPKI(1), and SHA-512 (2) looks like + +.code + _25._tcp.mail.example.com. TLSA 3 1 2 8BA8A336E... +.endd + +At the time of writing, &url(https://www.huque.com/bin/gen_tlsa) +is useful for quickly generating TLSA records. + For use with the DANE-TA model, server certificates must have a correct name (SubjectName or SubjectAltName). @@ -28913,7 +28977,9 @@ those who use &%hosts_require_ocsp%&, should consider the interaction with DANE 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. +The require variant will result in failure if the target host is not +DNSSEC-secured. To get DNSSEC-secured hostname resolution, use +the &%dnssec_request_domains%& router or transport option. DANE will only be usable if the target host has DNSSEC-secured MX, A and TLSA records. @@ -28943,7 +29009,7 @@ If DANE is requested and useable (see above) the following transport options are 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. +Currently the (router or transport options) &%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". @@ -30826,7 +30892,9 @@ the next &%local_parts%& test. .cindex "&ACL;" "virus scanning" .cindex "&ACL;" "scanning for viruses" This condition is available only when Exim is compiled with the -content-scanning extension. It causes the incoming message to be scanned for +content-scanning extension +and only after a DATA command. +It causes the incoming message to be scanned for viruses. For details, see chapter &<>&. .vitem &*mime_regex&~=&~*&<&'list&~of&~regular&~expressions'&> @@ -32614,6 +32682,15 @@ It supports a &"generic"& interface to scanners called via the shell, and specialized interfaces for &"daemon"& type virus scanners, which are resident in memory and thus are much faster. +.new +Since message data needs to have arrived, +the condition may be only called in ACL defined by +&%acl_smtp_data%&, +&%acl_smtp_data_prdr%&, +&%acl_smtp_mime%& or +&%acl_smtp_dkim%& +.wen + A timeout of 2 minutes is applied to a scanner call (by default); if it expires then a defer action is taken. @@ -39913,15 +39990,28 @@ RFC 6376 lists these tags as RECOMMENDED. 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. +.new +.cindex DKIM "selecting signature algorithms" +Individual classes of signature algorithm can be ignored by changing +the main options &%dkim_verify_hashes%& or &%dkim_verify_keytypes%&. +The &%dkim_verify_minimal%& option can be set to cease verification +processing for a message once the first passing signature is found. +.wen + .cindex authentication "expansion item" Performing verification sets up information used by the &$authresults$& expansion item. -The results of that verification are then made available to the +.new +For most purposes the default option settings suffice and the remainder +of this section can be ignored. +.wen + +The results of verification are made available to the &%acl_smtp_dkim%& ACL, which can examine and modify them. -By default, this ACL is called once for each -syntactically(!) correct signature in the incoming message. A missing ACL definition defaults to accept. +By default, the ACL is called once for each +syntactically(!) correct signature in the incoming message. If any ACL call does not accept, the message is not accepted. If a cutthrough delivery was in progress for the message, that is summarily dropped (having wasted the transmission effort). @@ -39932,11 +40022,11 @@ containing the signature status and its details are set up during the runtime of the ACL. Calling the ACL only for existing signatures is not sufficient to build -more advanced policies. For that reason, the global option -&%dkim_verify_signers%&, and a global expansion variable +more advanced policies. For that reason, the main option +&%dkim_verify_signers%&, and an expansion variable &%$dkim_signers%& exist. -The global option &%dkim_verify_signers%& can be set to a colon-separated +The main option &%dkim_verify_signers%& can be set to a colon-separated list of DKIM domains or identities for which the ACL &%acl_smtp_dkim%& is called. It is expanded when the message has been received. At this point, the expansion variable &%$dkim_signers%& already contains a colon-separated @@ -39974,7 +40064,7 @@ If multiple signatures match a domain (or identity), the ACL is called once for each matching signature. -Inside the &%acl_smtp_dkim%&, the following expansion variables are +Inside the DKIM ACL, the following expansion variables are available (from most to least important): @@ -40068,8 +40158,12 @@ DKIM signatures identified as having been signed with historic algorithms (currently, rsa-sha1) have permanently failed evaluation .endd -To enforce this you must have a DKIM ACL which checks this variable -and overwrites the &$dkim_verify_status$& variable as discussed above. +To enforce this you must either have a DKIM ACL which checks this variable +and overwrites the &$dkim_verify_status$& variable as discussed above, +.new +or have set the main option &%dkim_verify_hashes%& to exclude +processing of such signatures. +.wen .vitem &%$dkim_canon_body%& The body canonicalization method. One of 'relaxed' or 'simple'.