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,
-or with GnuTLS 3.1.3 or later, 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.
-
-Under OpenSSL 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, the smtp transport gains two options:
-- "hosts_require_ocsp"; a host-list for which an OCSP Stapling
-is requested and required for the connection to proceed. The default
-value is empty.
-- "hosts_request_ocsp"; a host-list for which (additionally) an OCSP
-Stapling is requested (but not necessarily verified). The default
-value is "*" meaning that requests are made unless configured
-otherwise.
-
-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).
-
-Note that the proof only covers the terminal server certificate,
-not any of the chain from CA to it.
-
-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 failure mode seen was the OCSP Signer cert expiring before the end
- of validity 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
--------------------------------------------------------------
Transport post-delivery actions
--------------------------------------------------------------
-An arbitrary per-transport string can be expanded on successful delivery,
+An arbitrary per-transport string can be expanded upon various transport events
and (for SMTP transports) a second string on deferrals caused by a host error.
+Additionally a main-section configuration option can be expanded on some
+per-message events.
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
+In order to use the feature, you must compile with
EXPERIMENTAL_TPDA=yes
in your Local/Makefile
-and define the expandable strings in the runtime config file, to
-be executed at end of delivery.
+and define one or both of
+- the tpda_event_action option in the transport
+- the delivery_event_action
+to be expanded when the event fires.
+
+A new variable, $tpda_event, is set to the event type when the
+expansion is done. The current list of events is:
+
+ msg:complete main per message
+ msg:delivery transport per recipient
+ msg:host:defer transport per attempt
+ msg:fail:delivery main per recipient
+ msg:fail:internal main per recipient
+ tcp:connect transport per connection
+ tcp:close transport per connection
+ tls:cert transport per certificate in verification chain
+ smtp:connect transport per connection
-Additionally, there are 6 more variables, available at end of
-delivery:
+The expansion is called for all event types, and should use the $tpda_event
+value to decide when to act. The variable data is a colon-separated
+list, describing an event tree.
-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
+There is an auxilary variable, $tpda_data, for which the
+content is event_dependent:
-In case of a deferral caused by a host-error:
-tpda_defer_errno Error number
-tpda_defer_errstr Error string possibly containing more details
+ msg:delivery smtp confirmation mssage
+ msg:host:defer error string
+ tls:cert verification chain depth
+ smtp:connect smtp banner
-The $router_name and $transport_name variables are also usable.
+The msg:host:defer event populates one extra variable, $tpda_defer_errno.
+The following variables are likely to be useful depending on the event type:
-To take action after successful deliveries, set the following option
-on any transport of interest.
+ router_name, transport_name
+ local_part, domain
+ host, host_address, host_port
+ tls_out_peercert
+ lookup_dnssec_authenticated, tls_out_dane
+ sending_ip_address, sending_port
+ message_exim_id
-tpda_delivery_action
An example might look like:
-tpda_delivery_action = \
-${lookup pgsql {SELECT * FROM record_Delivery( \
+tpda_event_action = ${if = {msg:delivery}{$tpda_event} \
+{${lookup pgsql {SELECT * FROM record_Delivery( \
'${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
+ '${quote_pgsql:$domain}', \
+ '${quote_pgsql:${lc:$local_part}}', \
+ '${quote_pgsql:$host_address}', \
+ '${quote_pgsql:${lc:$host}}', \
+ '${quote_pgsql:$message_exim_id}')}} \
+} {}}
+
+The string is expanded for each of the supported events 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:
+The expansion of the tpda_event_action option should normally
+return an empty string. Should it return anything else the
+following will be forced:
-tpda_host_defer_action
+ msg:delivery (ignored)
+ msg:host:defer (ignored)
+ msg:fail:delivery (ignored)
+ tcp:connect do not connect
+ tcp:close (ignored)
+ tls:cert refuse verification
+ smtp:connect close connection
-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
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
logwrite = Internal Server Address: $received_ip_address:$received_port
-4. Runtime issues to be aware of:
+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:
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
+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
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 / exim.git / blobdiff