X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/3ec3e3bba0e3a5bb855046805b7bcda6c0e327e3..66387a737208e277990b0cbfe58db3db419f34b2:/doc/doc-txt/experimental-spec.txt?ds=sidebyside diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt index 67737e9a6..855f9899a 100644 --- a/doc/doc-txt/experimental-spec.txt +++ b/doc/doc-txt/experimental-spec.txt @@ -1,263 +1,12 @@ -$Cambridge: exim/doc/doc-txt/experimental-spec.txt,v 1.4 2005/07/21 21:22:53 jetmore Exp $ - From time to time, experimental features may be added to Exim. While a feature is experimental, there will be a build-time option whose name starts "EXPERIMENTAL_" that must be set in order to include the feature. This file contains information -about experimenatal features, all of which are unstable and -liable to incompatibile change. - +about experimental features, all of which are unstable and +liable to incompatible change. -1. Yahoo DomainKeys support --------------------------------------------------------------- - -DomainKeys (DK) support is built into Exim using the -"libdomainkeys" reference library implementation. It is -available at - -http://domainkeys.sf.net - -You must build this library on your system and compile Exim -against it. To build Exim with DK support, add these lines to -your Local/Makefile: - -EXPERIMENTAL_DOMAINKEYS=yes -CFLAGS += -I/home/tom/exim-cvs/extra/libdomainkeys -LDFLAGS += -ldomainkeys -L/home/tom/exim-cvs/extra/libdomainkeys - -Remember to tweak the CFLAGS and LDFLAGS lines to match the -location of the libdomainkeys includes and lib on your system. - -The current experimental implementation supports two -independent functions: - -o Validate incoming DK-signed email. -o Sign outgoing email with DK. - -The former is implemented in the ACLs for SMTP, the latter as -an extension to the SMTP transport. That means both facilities -are limited to SMTP I/O. - - - -1) Validate incoming email - -Incoming messages are fed to the DK validation process as they -are received "on the wire". This happens synchronously to -Exim's buffering of the message in the spool. - -You must set "control = dk_verify" in one of the ACLs -preceding DATA (you will typically use acl_smtp_rcpt), at a -point where non-local, non-relay, non-submission mail is -processed. If that control flag is not set, the message will -NOT be verified. - -Example: - -warn log_message = Feeding message to DK validator. - control = dk_verify - -You can check for the outcome of the DK check in the ACL after -data (acl_smtp_data), using a number of ACL conditions and/or -expansion variables. - - - -1.1.) DK ACL conditions - - dk_sender_domains = - - This condition takes a domainlist as argument and - succeeds if the domain that DK has been verifying for is - found in the list. - - - dk_senders =
- - This condition takes an addresslist as argument and - succeeds if the address that DK has been verifying for - is found in the list. - - - dk_sender_local_parts = - - This condition takes a local_part list as argument - and succeeds if the domain that DK has been - verifying for is found in the list. - - - dk_status = - - This condition takes a list of keywords as argument, and - succeeds if one of the listed keywords matches the outcome - of the DK check. The available keywords are: - - good DK check succeeded, mail is verified. - bad DK check failed. - no signature Mail is not signed with DK. - no key Public key missing in target domain DNS. - bad format Public key available, but unuseable. - non-participant Target domain states not to participate in DK. - revoked The signing key has been revoked by the domain. - - - dk_policy = - - This condition takes a list of keywords as argument, and - succeeds if one of the listed keywords matches the policy - announced by the target domain. The available keywords - are: - - signsall The target domain signs all outgoing email. - testing The target domain is currently testing DK. - - - dk_domain_source = - - This condition takes a list of keywords as argument, and - succeeds if one of the listed keywords matches the - location where DK found the sender domain it verified for. - The available keywords are: - - from The domain came from the "From:" header. - sender The domain came from the "Sender:" header. - none DK was unable to find the responsible domain. - - - -1.2.) DK verification expansion variables - - $dk_sender_domain - - Contains the domain that DK has verified for. - - - $dk_sender - - Contains the address that DK has verified for. - - - $dk_sender_local_part - - Contains the local part that DK has verified for. - - - $dk_sender_source - - Contains the "source" of the above three variables, one of - - "from" The address came from the "From:" header. - "sender" The address came from the "Sender:" header. - - When DK was unable to find a valid address, this variable - is "0". - - - $dk_signsall - - Is "1" if the target domain signs all outgoing email, - "0" otherwise. - - - $dk_testing - - Is "1" if the target domain is testing DK, "0" otherwise. - - - $dk_is_signed - - Is "1" if the message is signed, "0" otherwise. - - - $dk_status - - Contains the outcome of the DK check as a string, commonly - used to add a "DomainKey-Status:" header to messages. Will - contain one of: - - good DK check succeeded, mail is verified. - bad DK check failed. - no signature Mail is not signed with DK. - no key Public key missing in target domain DNS. - bad format Public key available, but unuseable. - non-participant Target domain states not to participate in DK. - revoked The signing key has been revoked by the domain. - - - $dk_result - - Contains a human-readable result of the DK check, more - verbose than $dk_status. Useful for logging purposes. - - - -2) Sign outgoing email with DK - -Outgoing messages are signed just before Exim puts them "on -the wire". The only thing that happens after DK signing is -eventual TLS encryption. - -Signing is implemented by setting private options on the SMTP -transport. These options take (expandable) strings as -arguments. The most important variable to use in these -expansions is $dk_domain. It contains the domain that DK wants -to sign for. - - - dk_selector = [MANDATORY] - - This sets the key selector string. You can use the - $dk_domain expansion variable to look up a matching - selector. The result is put in the expansion variable - $dk_selector which should be used in the dk_private_key - option along with $dk_domain. - - - dk_private_key = [MANDATORY] - - This sets the private key to use. You SHOULD use the - $dk_domain and $dk_selector expansion variables to - determine the private key to use. The result can either - - o be a valid RSA private key in ASCII armor, including - line breaks. - o start with a slash, in which case it is treated as - a file that contains the private key. - o 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 dk_strict is set. - - - dk_canon = [OPTIONAL] - - This option sets the canonicalization method used when - signing a message. The DK draft currently supports two - methods: "simple" and "nofws". The option defaults to - "simple" when unset. - - - dk_strict = [OPTIONAL] - - This option defines how Exim behaves when signing a - message that should be signed fails for some reason. When - the expansion evaluates to either "1" or "true", Exim will - defer. Otherwise Exim will send the message unsigned. You - can and should use the $dk_domain and $dk_selector - expansion variables here. - - - dk_domain = [NOT RECOMMENDED] - - This option overrides DKs autodetection of the signing - domain. You should only use this option if you know what - you are doing. The result of the string expansion is also - put in $dk_domain. - - - - -2. Brightmail AntiSpam (BMI) suppport +Brightmail AntiSpam (BMI) support -------------------------------------------------------------- Brightmail AntiSpam is a commercial package. Please see @@ -293,14 +42,14 @@ These four steps are explained in more details below. 1) Adding support for BMI at compile time To compile with BMI support, you need to link Exim against - the Brighmail client SDK, consisting of a library + the Brightmail client SDK, consisting of a library (libbmiclient_single.so) and a header file (bmi_api.h). You'll also need to explicitly set a flag in the Makefile to include BMI support in the Exim binary. Both can be achieved with these lines in Local/Makefile: EXPERIMENTAL_BRIGHTMAIL=yes - CFLAGS=-DBRIGHTMAIL -I/path/to/the/dir/with/the/includefile + CFLAGS=-I/path/to/the/dir/with/the/includefile EXTRALIBS_EXIM=-L/path/to/the/dir/with/the/library -lbmiclient_single If you use other CFLAGS or EXTRALIBS_EXIM settings then @@ -543,138 +292,624 @@ These four steps are explained in more details below. -3. Sender Policy Framework (SPF) support +SRS (Sender Rewriting Scheme) Support -------------------------------------------------------------- -To learn more about SPF, visit http://spf.pobox.com. This -document does not explain the SPF fundamentals, you should -read and understand the implications of deploying SPF on your -system before doing so. - -SPF support is added via the libspf2 library. Visit - - http://www.libspf2.org/ - -to obtain a copy, then compile and install it. By default, -this will put headers in /usr/local/include and the static -library in /usr/local/lib. - -To compile Exim with SPF support, set these additional flags in -Local/Makefile: - -EXPERIMENTAL_SPF=yes -CFLAGS=-DSPF -I/usr/local/include -EXTRALIBS_EXIM=-L/usr/local/lib -lspf2 - -This assumes that the libspf2 files are installed in -their default locations. - -You can now run SPF checks in incoming SMTP by using the "spf" -ACL condition in either the MAIL, RCPT or DATA ACLs. When -using it in the RCPT ACL, you can make the checks dependend on -the RCPT address (or domain), so you can check SPF records -only for certain target domains. This gives you the -possibility to opt-out certain customers that do not want -their mail to be subject to SPF checking. - -The spf condition takes a list of strings on its right-hand -side. These strings describe the outcome of the SPF check for -which the spf condition should succeed. Valid strings are: - - o pass The SPF check passed, the sending host - is positively verified by SPF. - o fail The SPF check failed, the sending host - is NOT allowed to send mail for the domain - in the envelope-from address. - o softfail The SPF check failed, but the queried - domain can't absolutely confirm that this - is a forgery. - o none The queried domain does not publish SPF - records. - o neutral The SPF check returned a "neutral" state. - This means the queried domain has published - a SPF record, but wants to allow outside - servers to send mail under its domain as well. - o err_perm This indicates a syntax error in the SPF - record of the queried domain. This should be - treated like "none". - o err_temp This indicates a temporary error during all - processing, including Exim's SPF processing. - You may defer messages when this occurs. - -You can prefix each string with an exclamation mark to invert -is meaning, for example "!fail" will match all results but -"fail". The string list is evaluated left-to-right, in a -short-circuit fashion. When a string matches the outcome of -the SPF check, the condition succeeds. If none of the listed -strings matches the outcome of the SPF check, the condition -fails. +Exiscan currently includes SRS support via Miles Wilton's +libsrs_alt library. The current version of the supported +library is 0.5, there are reports of 1.0 working. -Here is a simple example to fail forgery attempts from domains -that publish SPF records: +In order to use SRS, you must get a copy of libsrs_alt from -/* ----------------- -deny message = $sender_host_address is not allowed to send mail from $sender_address_domain - spf = fail ---------------------- */ +https://opsec.eu/src/srs/ -You can also give special treatment to specific domains: +(not the original source, which has disappeared.) -/* ----------------- -deny message = AOL sender, but not from AOL-approved relay. - sender_domains = aol.com - spf = fail:neutral ---------------------- */ +Unpack the tarball, then refer to MTAs/README.EXIM +to proceed. You need to set -Explanation: AOL publishes SPF records, but is liberal and -still allows non-approved relays to send mail from aol.com. -This will result in a "neutral" state, while mail from genuine -AOL servers will result in "pass". The example above takes -this into account and treats "neutral" like "fail", but only -for aol.com. Please note that this violates the SPF draft. +EXPERIMENTAL_SRS=yes -When the spf condition has run, it sets up several expansion -variables. +in your Local/Makefile. - $spf_header_comment - This contains a human-readable string describing the outcome - of the SPF check. You can add it to a custom header or use - it for logging purposes. - $spf_received - This contains a complete SPF-Received: header that can be - added to the message. Please note that according to the SPF - draft, this header must be added at the top of the header - list. Please see section 10 on how you can do this. - $spf_result - This contains the outcome of the SPF check in string form, - one of pass, fail, softfail, none, neutral, err_perm or - err_temp. +DCC Support +-------------------------------------------------------------- +Distributed Checksum Clearinghouse; http://www.rhyolite.com/dcc/ - $spf_smtp_comment - This contains a string that can be used in a SMTP response - to the calling party. Useful for "fail". +*) Building exim +In order to build exim with DCC support add +EXPERIMENTAL_DCC=yes -4. SRS (Sender Rewriting Scheme) Support +to your Makefile. (Re-)build/install exim. exim -d should show +EXPERIMENTAL_DCC under "Support for". + + +*) Configuration + +In the main section of exim.cf add at least + dccifd_address = /usr/local/dcc/var/dccifd +or + dccifd_address = + +In the DATA ACL you can use the new condition + dcc = * + +After that "$dcc_header" contains the X-DCC-Header. + +Return values are: + fail for overall "R", "G" from dccifd + defer for overall "T" from dccifd + accept for overall "A", "S" from dccifd + +dcc = */defer_ok works as for spamd. + +The "$dcc_result" variable contains the overall result from DCC +answer. There will an X-DCC: header added to the mail. + +Usually you'll use + defer !dcc = * +to greylist with DCC. + +If you set, in the main section, + dcc_direct_add_header = true +then the dcc header will be added "in deep" and if the spool +file was already written it gets removed. This forces Exim to +write it again if needed. This helps to get the DCC Header +through to eg. SpamAssassin. + +If you want to pass even more headers in the middle of the +DATA stage you can set + $acl_m_dcc_add_header +to tell the DCC routines to add more information; eg, you might set +this to some results from ClamAV. Be careful. Header syntax is +not checked and is added "as is". + +In case you've troubles with sites sending the same queue items from several +hosts and fail to get through greylisting you can use +$acl_m_dcc_override_client_ip + +Setting $acl_m_dcc_override_client_ip to an IP address overrides the default +of $sender_host_address. eg. use the following ACL in DATA stage: + + warn set acl_m_dcc_override_client_ip = \ + ${lookup{$sender_helo_name}nwildlsearch{/etc/mail/multipleip_sites}{$value}{}} + condition = ${if def:acl_m_dcc_override_client_ip} + log_message = dbg: acl_m_dcc_override_client_ip set to \ + $acl_m_dcc_override_client_ip + +Then set something like +# cat /etc/mail/multipleip_sites +mout-xforward.gmx.net 82.165.159.12 +mout.gmx.net 212.227.15.16 + +Use a reasonable IP. eg. one the sending cluster actually uses. + + + +DMARC Support -------------------------------------------------------------- -Exiscan currently includes SRS support via Miles Wilton's -libsrs_alt library. The current version of the supported -library is 0.5. +DMARC combines feedback from SPF, DKIM, and header From: in order +to attempt to provide better indicators of the authenticity of an +email. This document does not explain the fundamentals, you +should read and understand how it works by visiting the website at +http://www.dmarc.org/. + +DMARC support is added via the libopendmarc library. Visit: + + http://sourceforge.net/projects/opendmarc/ + +to obtain a copy, or find it in your favorite rpm package +repository. If building from source, this description assumes +that headers will be in /usr/local/include, and that the libraries +are in /usr/local/lib. + +1. To compile Exim with DMARC support, you must first enable SPF. +Please read the Local/Makefile comments on enabling the SUPPORT_SPF +feature. You must also have DKIM support, so you cannot set the +DISABLE_DKIM feature. Once both of those conditions have been met +you can enable DMARC in Local/Makefile: + +EXPERIMENTAL_DMARC=yes +LDFLAGS += -lopendmarc +# CFLAGS += -I/usr/local/include +# LDFLAGS += -L/usr/local/lib + +The first line sets the feature to include the correct code, and +the second line says to link the libopendmarc libraries into the +exim binary. The commented out lines should be uncommented if you +built opendmarc from source and installed in the default location. +Adjust the paths if you installed them elsewhere, but you do not +need to uncomment them if an rpm (or you) installed them in the +package controlled locations (/usr/include and /usr/lib). + + +2. Use the following global settings to configure DMARC: + +Optional: +dmarc_tld_file Defines the location of a text file of valid + top level domains the opendmarc library uses + during domain parsing. Maintained by Mozilla, + the most current version can be downloaded + from a link at http://publicsuffix.org/list/. + If unset, "/etc/exim/opendmarc.tlds" (hardcoded) + is used. + +Optional: +dmarc_history_file Defines the location of a file to log results + of dmarc verification on inbound emails. The + contents are importable by the opendmarc tools + which will manage the data, send out DMARC + reports, and expire the data. Make sure the + directory of this file is writable by the user + exim runs as. + +dmarc_forensic_sender The email address to use when sending a + forensic report detailing alignment failures + if a sender domain's dmarc record specifies it + and you have configured Exim to send them. + Default: do-not-reply@$default_hostname + + +3. By default, the DMARC processing will run for any remote, +non-authenticated user. It makes sense to only verify DMARC +status of messages coming from remote, untrusted sources. You can +use standard conditions such as hosts, senders, etc, to decide that +DMARC verification should *not* be performed for them and disable +DMARC with a control setting: + + control = dmarc_disable_verify + +A DMARC record can also specify a "forensic address", which gives +exim an email address to submit reports about failed alignment. +Exim does not do this by default because in certain conditions it +results in unintended information leakage (what lists a user might +be subscribed to, etc). You must configure exim to submit forensic +reports to the owner of the domain. If the DMARC record contains a +forensic address and you specify the control statement below, then +exim will send these forensic emails. It's also advised that you +configure a dmarc_forensic_sender because the default sender address +construction might be inadequate. + + control = dmarc_enable_forensic + +(AGAIN: You can choose not to send these forensic reports by simply +not putting the dmarc_enable_forensic control line at any point in +your exim config. If you don't tell it to send them, it will not +send them.) + +There are no options to either control. Both must appear before +the DATA acl. + + +4. You can now run DMARC checks in incoming SMTP by using the +"dmarc_status" ACL condition in the DATA ACL. You are required to +call the spf condition first in the ACLs, then the "dmarc_status" +condition. Putting this condition in the ACLs is required in order +for a DMARC check to actually occur. All of the variables are set +up before the DATA ACL, but there is no actual DMARC check that +occurs until a "dmarc_status" condition is encountered in the ACLs. + +The dmarc_status condition takes a list of strings on its +right-hand side. These strings describe recommended action based +on the DMARC check. To understand what the policy recommendations +mean, refer to the DMARC website above. Valid strings are: + + o accept The DMARC check passed and the library recommends + accepting the email. + o reject The DMARC check failed and the library recommends + rejecting the email. + o quarantine The DMARC check failed and the library recommends + keeping it for further inspection. + o none The DMARC check passed and the library recommends + no specific action, neutral. + o norecord No policy section in the DMARC record for this + sender domain. + o nofrom Unable to determine the domain of the sender. + o temperror Library error or dns error. + o off The DMARC check was disabled for this email. + +You can prefix each string with an exclamation mark to invert its +meaning, for example "!accept" will match all results but +"accept". The string list is evaluated left-to-right in a +short-circuit fashion. When a string matches the outcome of the +DMARC check, the condition succeeds. If none of the listed +strings matches the outcome of the DMARC check, the condition +fails. -In order to use SRS, you must get a copy of libsrs_alt from +Of course, you can also use any other lookup method that Exim +supports, including LDAP, Postgres, MySQL, etc, as long as the +result is a list of colon-separated strings. + +Several expansion variables are set before the DATA ACL is +processed, and you can use them in this ACL. The following +expansion variables are available: + + o $dmarc_status + This is a one word status indicating what the DMARC library + thinks of the email. It is a combination of the results of + DMARC record lookup and the SPF/DKIM/DMARC processing results + (if a DMARC record was found). The actual policy declared + in the DMARC record is in a separate expansion variable. + + o $dmarc_status_text + This is a slightly longer, human readable status. + + o $dmarc_used_domain + This is the domain which DMARC used to look up the DMARC + policy record. + + o $dmarc_domain_policy + This is the policy declared in the DMARC record. Valid values + are "none", "reject" and "quarantine". It is blank when there + is any error, including no DMARC record. + + o $dmarc_ar_header + This is the entire Authentication-Results header which you can + add using an add_header modifier. + + +5. How to enable DMARC advanced operation: +By default, Exim's DMARC configuration is intended to be +non-intrusive and conservative. To facilitate this, Exim will not +create any type of logging files without explicit configuration by +you, the admin. Nor will Exim send out any emails/reports about +DMARC issues without explicit configuration by you, the admin (other +than typical bounce messages that may come about due to ACL +processing or failure delivery issues). + +In order to log statistics suitable to be imported by the opendmarc +tools, you need to: +a. Configure the global setting dmarc_history_file. +b. Configure cron jobs to call the appropriate opendmarc history + import scripts and truncating the dmarc_history_file. + +In order to send forensic reports, you need to: +a. Configure the global setting dmarc_forensic_sender. +b. Configure, somewhere before the DATA ACL, the control option to + enable sending DMARC forensic reports. + + +6. Example usage: +(RCPT ACL) + warn domains = +local_domains + hosts = +local_hosts + control = dmarc_disable_verify + + warn !domains = +screwed_up_dmarc_records + control = dmarc_enable_forensic + + warn condition = (lookup if destined to mailing list) + set acl_m_mailing_list = 1 + +(DATA ACL) + warn dmarc_status = accept : none : off + !authenticated = * + log_message = DMARC DEBUG: $dmarc_status $dmarc_used_domain + add_header = $dmarc_ar_header + + warn dmarc_status = !accept + !authenticated = * + log_message = DMARC DEBUG: '$dmarc_status' for $dmarc_used_domain + + warn dmarc_status = quarantine + !authenticated = * + set $acl_m_quarantine = 1 + # Do something in a transport with this flag variable + + deny condition = ${if eq{$dmarc_domain_policy}{reject}} + condition = ${if eq{$acl_m_mailing_list}{1}} + message = Messages from $dmarc_used_domain break mailing lists + + deny dmarc_status = reject + !authenticated = * + message = Message from $dmarc_used_domain failed sender's DMARC policy, REJECT + + + +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. + +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, https://www.huque.com/bin/gen_tlsa +is useful for quickly generating TLSA records; and commands like + + openssl x509 -in -pubkey -noout /dev/null \ + | openssl sha512 \ + | awk '{print $2}' + +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: + + hosts_request_ocsp = ${if or { {= {0}{$tls_out_tlsa_usage}} \ + {= {4}{$tls_out_tlsa_usage}} } \ + {*}{}} + +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. +[ should they be domain-based rather than host-based? ] + +Hosts_require_dane 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: + hosts_require_tls + tls_verify_hosts + tls_try_verify_hosts + tls_verify_certificates + tls_crl + tls_verify_cert_hostnames + +If DANE is not usable, whether requested or not, and CA-anchored +verification evaluation is wanted, the above variables should be set +appropriately. + +Currently dnssec_request_domains must be active (need to think about that) +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 $tls_out_dane which will have "yes" if +verification succeeded using DANE and "no" otherwise (only useful +in combination with EXPERIMENTAL_EVENT), and a new variable +$tls_out_tlsa_usage (detailed above). + +Under GnuTLS, DANE is only supported from versin 3.0.0 onwards + + + +DSN extra information +--------------------- +If compiled with EXPERIMENTAL_DSN_INFO extra information will be added +to DSN fail messages ("bounces"), when available. The intent is to aid +tracing of specific failing messages, when presented with a "bounce" +complaint and needing to search logs. -http://srs.mirtol.com/ -Unpack the tarball, then refer to MTAs/README.EXIM -to proceed. You need to set +The remote MTA IP address, with port number if nonstandard. +Example: + Remote-MTA: X-ip; [127.0.0.1]:587 +Rationale: + Several addresses may correspond to the (already available) + dns name for the remote MTA. -EXPERIMENTAL_SRS=yes +The remote MTA connect-time greeting. +Example: + X-Remote-MTA-smtp-greeting: X-str; 220 the.local.host.name ESMTP Exim x.yz Tue, 2 Mar 1999 09:44:33 +0000 +Rationale: + This string sometimes presents the remote MTA's idea of its + own name, and sometimes identifies the MTA software. -in your Local/Makefile. +The remote MTA response to HELO or EHLO. +Example: + X-Remote-MTA-helo-response: X-str; 250-the.local.host.name Hello localhost [127.0.0.1] +Limitations: + Only the first line of a multiline response is recorded. +Rationale: + This string sometimes presents the remote MTA's view of + the peer IP connecting to it. + +The reporting MTA detailed diagnostic. +Example: + X-Exim-Diagnostic: X-str; SMTP error from remote mail server after RCPT TO:: 550 hard error +Rationale: + This string sometimes give extra information over the + existing (already available) Diagnostic-Code field. + + +Note that non-RFC-documented field names and data types are used. + + +LMDB Lookup support +------------------- +LMDB is an ultra-fast, ultra-compact, crash-proof key-value embedded data store. +It is modeled loosely on the BerkeleyDB API. You should read about the feature +set as well as operation modes at https://symas.com/products/lightning-memory-mapped-database/ + +LMDB single key lookup support is provided by linking to the LMDB C library. +The current implementation does not support writing to the LMDB database. + +Visit https://github.com/LMDB/lmdb to download the library or find it in your +operating systems package repository. + +If building from source, this description assumes that headers will be in +/usr/local/include, and that the libraries are in /usr/local/lib. + +1. In order to build exim with LMDB lookup support add or uncomment + +EXPERIMENTAL_LMDB=yes + +to your Local/Makefile. (Re-)build/install exim. exim -d should show +Experimental_LMDB in the line "Support for:". + +EXPERIMENTAL_LMDB=yes +LDFLAGS += -llmdb +# CFLAGS += -I/usr/local/include +# LDFLAGS += -L/usr/local/lib + +The first line sets the feature to include the correct code, and +the second line says to link the LMDB libraries into the +exim binary. The commented out lines should be uncommented if you +built LMDB from source and installed in the default location. +Adjust the paths if you installed them elsewhere, but you do not +need to uncomment them if an rpm (or you) installed them in the +package controlled locations (/usr/include and /usr/lib). + +2. Create your LMDB files, you can use the mdb_load utility which is +part of the LMDB distribution our your favourite language bindings. + +3. Add the single key lookups to your exim.conf file, example lookups +are below. + +${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}} +${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}fail} +${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}} + + +Queuefile transport +------------------- +Queuefile is a pseudo transport which does not perform final delivery. +It simply copies the exim spool files out of the spool directory into +an external directory retaining the exim spool format. + +The spool files can then be processed by external processes and then +requeued into exim spool directories for final delivery. + +The motivation/inspiration for the transport is to allow external +processes to access email queued by exim and have access to all the +information which would not be available if the messages were delivered +to the process in the standard email formats. + +The mailscanner package is one of the processes that can take advantage +of this transport to filter email. + +The transport can be used in the same way as the other existing transports, +i.e by configuring a router to route mail to a transport configured with +the queuefile driver. + +The transport only takes one option: + +* directory - This is used to specify the directory messages should be +copied to + +The generic transport options (body_only, current_directory, disable_logging, +debug_print, delivery_date_add, envelope_to_add, event_action, group, +headers_add, headers_only, headers_remove, headers_rewrite, home_directory, +initgroups, max_parallel, message_size_limit, rcpt_include_affixes, +retry_use_local_part, return_path, return_path_add, shadow_condition, +shadow_transport, transport_filter, transport_filter_timeout, user) are +ignored. + +Sample configuration: + +(Router) + +scan: + driver = accept + transport = scan + +(Transport) + +scan: + driver = queuefile + directory = /var/spool/baruwa-scanner/input + + +In order to build exim with Queuefile transport support add or uncomment + +EXPERIMENTAL_QUEUEFILE=yes + +to your Local/Makefile. (Re-)build/install exim. exim -d should show +Experimental_QUEUEFILE in the line "Support for:". --------------------------------------------------------------