liable to incompatible change.
-PRDR support
---------------------------------------------------------------
-
-Per-Recipient Data Reponse is an SMTP extension proposed by Eric Hall
-in a (now-expired) IETF draft from 2007. It's not hit mainstream
-use, but has apparently been implemented in the META1 MTA.
-
-There is mention at http://mail.aegee.org/intern/sendmail.html
-of a patch to sendmail "to make it PRDR capable".
-
- ref: http://www.eric-a-hall.com/specs/draft-hall-prdr-00.txt
-
-If Exim is built with EXPERIMENTAL_PRDR there is a new config
-boolean "prdr_enable" which controls whether PRDR is advertised
-as part of an EHLO response, a new "acl_data_smtp_prdr" ACL
-(called for each recipient, after data arrives but before the
-data ACL), and a new smtp transport option "hosts_try_prdr".
-
-PRDR may be used to support per-user content filtering. Without it
-one must defer any recipient after the first that has a different
-content-filter configuration. With PRDR, the RCPT-time check
-for this can be disabled when the MAIL-time $smtp_command included
-"PRDR". Any required difference in behaviour of the main DATA-time
-ACL should however depend on the PRDR-time ACL having run, as Exim
-will avoid doing so in some situations (eg. single-recipient mails).
-
-
-
-OCSP Stapling support
---------------------------------------------------------------
-
-X.509 PKI certificates expire and can be revoked; to handle this, the
-clients need some way to determine if a particular certificate, from a
-particular Certificate Authority (CA), is still valid. There are three
-main ways to do so.
-
-The simplest way is to serve up a Certificate Revocation List (CRL) with
-an ordinary web-server, regenerating the CRL before it expires. The
-downside is that clients have to periodically re-download a potentially
-huge file from every certificate authority it knows of.
-
-The way with most moving parts at query time is Online Certificate
-Status Protocol (OCSP), where the client verifies the certificate
-against an OCSP server run by the CA. This lets the CA track all
-usage of the certs. This requires running software with access to the
-private key of the CA, to sign the responses to the OCSP queries. OCSP
-is based on HTTP and can be proxied accordingly.
-
-The only widespread OCSP server implementation (known to this writer)
-comes as part of OpenSSL and aborts on an invalid request, such as
-connecting to the port and then disconnecting. This requires
-re-entering the passphrase each time some random client does this.
-
-The third way is OCSP Stapling; in this, the server using a certificate
-issued by the CA periodically requests an OCSP proof of validity from
-the OCSP server, then serves it up inline as part of the TLS
-negotiation. This approach adds no extra round trips, does not let the
-CA track users, scales well with number of certs issued by the CA and is
-resilient to temporary OCSP server failures, as long as the server
-starts retrying to fetch an OCSP proof some time before its current
-proof expires. The downside is that it requires server support.
-
-If Exim is built with EXPERIMENTAL_OCSP and it was built with OpenSSL,
-then it gains a new global option: "tls_ocsp_file".
-
-The file specified therein is expected to be in DER format, and contain
-an OCSP proof. Exim will serve it as part of the TLS handshake. This
-option will be re-expanded for SNI, if the tls_certificate option
-contains $tls_sni, as per other TLS options.
-
-Exim does not at this time implement any support for fetching a new OCSP
-proof. The burden is on the administrator to handle this, outside of
-Exim. The file specified should be replaced atomically, so that the
-contents are always valid. Exim will expand the "tls_ocsp_file" option
-on each connection, so a new file will be handled transparently on the
-next connection.
-
-Exim will check for a valid next update timestamp in the OCSP proof;
-if not present, or if the proof has expired, it will be ignored.
-
-Also, given EXPERIMENTAL_OCSP and OpenSSL, the smtp transport gains
-a "hosts_require_ocsp" option; a host-list for which an OCSP Stapling
-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.
-
-
-
-
Brightmail AntiSpam (BMI) suppport
--------------------------------------------------------------
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
$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
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;
+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
o $dmarc_status
This is a one word status indicating what the DMARC library
- thinks of the email.
+ 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.
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.
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 = *
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
set acl_c_spam_host = ${lookup redis{GET...}}
+Proxy Protocol Support
+--------------------------------------------------------------
+
+Exim now has Experimental "Proxy Protocol" support. It was built on
+specifications from:
+http://haproxy.1wt.eu/download/1.5/doc/proxy-protocol.txt
+Above URL revised May 2014 to change version 2 spec:
+http://git.1wt.eu/web?p=haproxy.git;a=commitdiff;h=afb768340c9d7e50d8e
+
+The purpose of this function is so that an application load balancer,
+such as HAProxy, can sit in front of several Exim servers and Exim
+will log the IP that is connecting to the proxy server instead of
+the IP of the proxy server when it connects to Exim. It resets the
+$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 (internal) src IP of the proxy server
+ making the connection to the Exim server.
+proxy_host_port The (internal) src port the proxy server is
+ using to connect to the Exim server.
+proxy_target_address The dest (public) IP of the remote host to
+ the proxy server.
+proxy_target_port The dest port the remote host is using to
+ connect to the proxy server.
+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
+
+ # Possibly more clear
+ warn logwrite = Remote Source Address: $sender_host_address:$sender_host_port
+ logwrite = Proxy Target Address: $proxy_target_address:$proxy_target_port
+ logwrite = Proxy Internal Address: $proxy_host_address:$proxy_host_port
+ logwrite = Internal Server Address: $received_ip_address:$received_port
+
+
+4. Recommended ACL additions:
+ - 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.
+ - With the smtp_accept_max_per_host set so high, you lose the ability
+ to protect your server from massive numbers of inbound connections
+ from one IP. In order to prevent your server from being DOS'd, you
+ need to add a per connection ratelimit to your connect ACL. I
+ suggest something like this:
+
+ # Set max number of connections per host
+ LIMIT = 5
+ # Or do some kind of IP lookup in a flat file or database
+ # LIMIT = ${lookup{$sender_host_address}iplsearch{/etc/exim/proxy_limits}}
+
+ defer message = Too many connections from this IP right now
+ ratelimit = LIMIT / 5s / per_conn / strict
+
+
+5. Runtime issues to be aware of:
+ - 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!
+
+6. 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
+
+
+DSN Support
+--------------------------------------------------------------
+
+DSN Support tries to add RFC 3461 support to Exim. It adds support for
+*) the additional parameters for MAIL FROM and RCPT TO
+*) RFC complient MIME DSN messages for all of
+ success, failure and delay notifications
+*) dsn_advertise_hosts main option to select which hosts are able
+ to use the extension
+*) dsn_lasthop router switch to end DSN processing
+
+In case of failure reports this means that the last three parts, the message body
+intro, size info and final text, of the defined template are ignored since there is no
+logical place to put them in the MIME message.
+
+All the other changes are made without changing any defaults
+
+Building exim:
+--------------
+
+Define
+EXPERIMENTAL_DSN=YES
+in your Local/Makefile.
+
+Configuration:
+--------------
+All DSNs are sent in MIME format if you built exim with EXPERIMENTAL_DSN=YES
+No option needed to activate it, and no way to turn it off.
+
+Failure and delay DSNs are triggered as usual except a sender used NOTIFY=...
+to prevent them.
+
+Support for Success DSNs is added and activated by NOTIFY=SUCCESS by clients.
+
+Add
+dsn_advertise_hosts = *
+or a more restrictive host_list to announce DSN in EHLO answers
+
+Those hosts can then use NOTIFY,ENVID,RET,ORCPT options.
+
+If a message is relayed to a DSN aware host without changing the envelope
+recipient the options are passed along and no success DSN is generated.
+
+A redirect router will always trigger a success DSN if requested and the DSN
+options are not passed any further.
+
+A success DSN always contains the recipient address as submitted by the
+client as required by RFC. Rewritten addresses are never exposed.
+
+If you used DSN patch up to 1.3 before remove all "dsn_process" switches from
+your routers since you don't need them anymore. There is no way to "gag"
+success DSNs anymore. Announcing DSN means answering as requested.
+
+You can prevent Exim from passing DSN options along to other DSN aware hosts by defining
+dsn_lasthop
+in a router. Exim will then send the success DSN himself if requested as if
+the next hop does not support DSN.
+Adding it to a redirect router makes no difference.
+
+Certificate name checking
+--------------------------------------------------------------
+The X509 certificates used for TLS are supposed be verified
+that they are owned by the expected host. The coding of TLS
+support to date has not made these checks.
+
+If built with EXPERIMENTAL_CERTNAMES defined, code is
+included to do so, and a new smtp transport option
+"tls_verify_cert_hostname" supported which takes a list of
+names for which the checks must be made. The host must
+also be in "tls_verify_hosts".
+
+Both Subject and Subject-Alternate-Name certificate fields
+are supported, as are wildcard certificates (limited to
+a single wildcard being the initial component of a 3-or-more
+component FQDN).
+
+
--------------------------------------------------------------
End of file
git://git.exim.org / users / heiko / exim.git / blobdiff