X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/57233af5f91cdca9a0232a71fab2d12a538cb1a6..887291d23b561d0bb8cf43db80c191810e2d8ce3:/doc/doc-txt/experimental-spec.txt diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt index 385f0526e..265e1211b 100644 --- a/doc/doc-txt/experimental-spec.txt +++ b/doc/doc-txt/experimental-spec.txt @@ -92,10 +92,25 @@ is requested and required for the connection to proceed. The host(s) should also be in "hosts_require_tls", and "tls_verify_certificates" configured for the transport. +For the client to be able to verify the stapled OCSP the server must +also supply, in its stapled information, any intermediate +certificates for the chain leading to the OCSP proof from the signer +of the server certificate. There may be zero or one such. These +intermediate certificates should be added to the server OCSP stapling +file (named by tls_ocsp_file). + At this point in time, we're gathering feedback on use, to determine if it's worth adding complexity to the Exim daemon to periodically re-fetch OCSP files and somehow handling multiple files. + A helper script "ocsp_fetch.pl" for fetching a proof from a CA + OCSP server is supplied. The server URL may be included in the + server certificate, if the CA is helpful. + + One fail mode seen was the OCSP Signer cert expiring before the end + of vailidity of the OCSP proof. The checking done by Exim/OpenSSL + noted this as invalid overall, but the re-fetch script did not. + @@ -437,15 +452,21 @@ which the spf condition should succeed. Valid strings are: 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 + This should be treated like "none". + o 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) + o 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) + o err_temp Same as permerror, deprecated in 4.83, will be + removed in a future release. + o err_perm Same as temperror, deprecated in 4.83, will be + removed in a future release. You can prefix each string with an exclamation mark to invert -is meaning, for example "!fail" will match all results but +its 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 @@ -495,8 +516,8 @@ variables. $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. + one of pass, fail, softfail, none, neutral, permerror or + temperror. $spf_smtp_comment This contains a string that can be used in a SMTP response @@ -627,6 +648,507 @@ mout.gmx.net 212.227.15.16 Use a reasonable IP. eg. one the sending cluster acutally uses. +DMARC Support +-------------------------------------------------------------- + +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 above section on enabling the EXPERIMENTAL_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: + +Required: +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/. + +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_forensic_enable + +(AGAIN: You can choose not to send these forensic reports by simply +not putting the dmarc_forensic_enable 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. + +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 $domain_used_domain failed sender's DMARC policy, REJECT + + + +Transport post-delivery actions +-------------------------------------------------------------- + +An arbitrary per-transport string can be expanded on successful delivery, +and (for SMTP transports) a second string on deferrals caused by a host error. +This feature may be used, for example, to write exim internal log information +(not available otherwise) into a database. + +In order to use the feature, you must set + +EXPERIMENTAL_TPDA=yes + +in your Local/Makefile + +and define the expandable strings in the runtime config file, to +be executed at end of delivery. + +Additionally, there are 6 more variables, available at end of +delivery: + +tpda_delivery_ip IP of host, which has accepted delivery +tpda_delivery_port Port of remote host which has accepted delivery +tpda_delivery_fqdn FQDN of host, which has accepted delivery +tpda_delivery_local_part local part of address being delivered +tpda_delivery_domain domain part of address being delivered +tpda_delivery_confirmation SMTP confirmation message + +In case of a deferral caused by a host-error: +tpda_defer_errno Error number +tpda_defer_errstr Error string possibly containing more details + +The $router_name and $transport_name variables are also usable. + + +To take action after successful deliveries, set the following option +on any transport of interest. + +tpda_delivery_action + +An example might look like: + +tpda_delivery_action = \ +${lookup pgsql {SELECT * FROM record_Delivery( \ + '${quote_pgsql:$sender_address_domain}',\ + '${quote_pgsql:${lc:$sender_address_local_part}}', \ + '${quote_pgsql:$tpda_delivery_domain}', \ + '${quote_pgsql:${lc:$tpda_delivery_local_part}}', \ + '${quote_pgsql:$tpda_delivery_ip}', \ + '${quote_pgsql:${lc:$tpda_delivery_fqdn}}', \ + '${quote_pgsql:$message_exim_id}')}} + +The string is expanded after the delivery completes and any +side-effects will happen. The result is then discarded. +Note that for complex operations an ACL expansion can be used. + + +In order to log host deferrals, add the following option to an SMTP +transport: + +tpda_host_defer_action + +This is a private option of the SMTP transport. It is intended to +log failures of remote hosts. It is executed only when exim has +attempted to deliver a message to a remote host and failed due to +an error which doesn't seem to be related to the individual +message, sender, or recipient address. +See section 47.2 of the exim documentation for more details on how +this is determined. + +Example: + +tpda_host_defer_action = \ +${lookup mysql {insert into delivlog set \ + msgid = '${quote_mysql:$message_exim_id}', \ + senderlp = '${quote_mysql:${lc:$sender_address_local_part}}', \ + senderdom = '${quote_mysql:$sender_address_domain}', \ + delivlp = '${quote_mysql:${lc:$tpda_delivery_local_part}}', \ + delivdom = '${quote_mysql:$tpda_delivery_domain}', \ + delivip = '${quote_mysql:$tpda_delivery_ip}', \ + delivport = '${quote_mysql:$tpda_delivery_port}', \ + delivfqdn = '${quote_mysql:$tpda_delivery_fqdn}', \ + deliverrno = '${quote_mysql:$tpda_defer_errno}', \ + deliverrstr = '${quote_mysql:$tpda_defer_errstr}' \ + }} + + +Redis Lookup +-------------------------------------------------------------- + +Redis is open source advanced key-value data store. This document +does not explain the fundamentals, you should read and understand how +it works by visiting the website at http://www.redis.io/. + +Redis lookup support is added via the hiredis library. Visit: + + https://github.com/redis/hiredis + +to obtain a copy, 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 Redis lookup support add + +EXPERIMENTAL_REDIS=yes + +to your Local/Makefile. (Re-)build/install exim. exim -d should show +Experimental_Redis in the line "Support for:". + +EXPERIMENTAL_REDIS=yes +LDFLAGS += -lhiredis +# 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 hiredis libraries into the +exim binary. The commented out lines should be uncommented if you +built hiredis 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 Redis lookup support: + +Required: +redis_servers This option provides a list of Redis servers + and associated connection data, to be used in + conjunction with redis lookups. The option is + only available if Exim is configured with Redis + support. + +For example: + +redis_servers = 127.0.0.1/10/ - using database 10 with no password +redis_servers = 127.0.0.1//password - to make use of the default database of 0 with a password +redis_servers = 127.0.0.1// - for default database of 0 with no password + +3. Once you have the Redis servers defined you can then make use of the +experimental Redis lookup by specifying ${lookup redis{}} in a lookup query. + +4. Example usage: + +(Host List) +hostlist relay_from_ips = <\n ${lookup redis{SMEMBERS relay_from_ips}} + +Where relay_from_ips is a Redis set which contains entries such as "192.168.0.0/24" "10.0.0.0/8" and so on. +The result set is returned as +192.168.0.0/24 +10.0.0.0/8 +.. +. + +(Domain list) +domainlist virtual_domains = ${lookup redis {HGET $domain domain}} + +Where $domain is a hash which includes the key 'domain' and the value '$domain'. + +(Adding or updating an existing key) +set acl_c_spammer = ${if eq{${lookup redis{SPAMMER_SET}}}{OK}} + +Where SPAMMER_SET is a macro and it is defined as + +"SET SPAMMER " + +(Getting a value from Redis) + +set acl_c_spam_host = ${lookup redis{GET...}} + + +Proxy Protocol Support +-------------------------------------------------------------- + +Exim now has Experimental "Proxy Protocol" support. It was built on +specifications from: +http://haproxy.1wt.eu/download/1.5/doc/proxy-protocol.txt + +The purpose of this function is so that an application load balancer, +such as HAProxy, can sit in front of several Exim servers and Exim +will log the IP that is connecting to the proxy server instead of +the IP of the proxy server when it connects to Exim. It resets the +$sender_address_host and $sender_address_port to the IP:port of the +connection to the proxy. It also re-queries the DNS information for +this new IP address so that the original sender's hostname and IP +get logged in the Exim logfile. There is no logging if a host passes or +fails Proxy Protocol negotiation, but it can easily be determined and +recorded in an ACL (example is below). + +1. To compile Exim with Proxy Protocol support, put this in +Local/Makefile: + +EXPERIMENTAL_PROXY=yes + +2. Global configuration settings: + +proxy_required_hosts = HOSTLIST + +The proxy_required_hosts option will require any IP in that hostlist +to use Proxy Protocol. The specification of Proxy Protocol is very +strict, and if proxy negotiation fails, Exim will not allow any SMTP +command other than QUIT. (See end of this section for an example.) +The option is expanded when used, so it can be a hostlist as well as +string of IP addresses. Since it is expanded, specifying an alternate +separator is supported for ease of use with IPv6 addresses. + +To log the IP of the proxy in the incoming logline, add: + log_selector = +proxy + +A default incoming logline (wrapped for appearance) will look like this: + + 2013-11-04 09:25:06 1VdNti-0001OY-1V <= me@example.net + H=mail.example.net [1.2.3.4] P=esmtp S=433 + +With the log selector enabled, an email that was proxied through a +Proxy Protocol server at 192.168.1.2 will look like this: + + 2013-11-04 09:25:06 1VdNti-0001OY-1V <= me@example.net + H=mail.example.net [1.2.3.4] P=esmtp PRX=192.168.1.2 S=433 + +3. In the ACL's the following expansion variables are available. + +proxy_host_address The src IP of the proxy server making the connection +proxy_host_port The src port the proxy server is using +proxy_session Boolean, yes/no, the connected host is required to use + Proxy Protocol. + +There is no expansion for a failed proxy session, however you can detect +it by checking if $proxy_session is true but $proxy_host is empty. As +an example, in my connect ACL, I have: + + warn condition = ${if and{ {bool{$proxy_session}} \ + {eq{$proxy_host_address}{}} } } + log_message = Failed required proxy protocol negotiation \ + from $sender_host_name [$sender_host_address] + + warn condition = ${if and{ {bool{$proxy_session}} \ + {!eq{$proxy_host_address}{}} } } + # But don't log health probes from the proxy itself + condition = ${if eq{$proxy_host_address}{$sender_host_address} \ + {false}{true}} + log_message = Successfully proxied from $sender_host_name \ + [$sender_host_address] through proxy protocol \ + host $proxy_host_address + +4. Runtime issues to be aware of: + - Since the real connections are all coming from your proxy, and the + per host connection tracking is done before Proxy Protocol is + evaluated, smtp_accept_max_per_host must be set high enough to + handle all of the parallel volume you expect per inbound proxy. + - The proxy has 3 seconds (hard-coded in the source code) to send the + required Proxy Protocol header after it connects. If it does not, + the response to any commands will be: + "503 Command refused, required Proxy negotiation failed" + - If the incoming connection is configured in Exim to be a Proxy + Protocol host, but the proxy is not sending the header, the banner + does not get sent until the timeout occurs. If the sending host + sent any input (before the banner), this causes a standard Exim + synchronization error (i.e. trying to pipeline before PIPELINING + was advertised). + - This is not advised, but is mentioned for completeness if you have + a specific internal configuration that you want this: If the Exim + server only has an internal IP address and no other machines in your + organization will connect to it to try to send email, you may + simply set the hostlist to "*", however, this will prevent local + mail programs from working because that would require mail from + localhost to use Proxy Protocol. Again, not advised! + +5. Example of a refused connection because the Proxy Protocol header was +not sent from a host configured to use Proxy Protocol. In the example, +the 3 second timeout occurred (when a Proxy Protocol banner should have +been sent), the banner was displayed to the user, but all commands are +rejected except for QUIT: + +# nc mail.example.net 25 +220-mail.example.net, ESMTP Exim 4.82+proxy, Mon, 04 Nov 2013 10:45:59 +220 -0800 RFC's enforced +EHLO localhost +503 Command refused, required Proxy negotiation failed +QUIT +221 mail.example.net closing connection + + + -------------------------------------------------------------- End of file --------------------------------------------------------------