+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).
+
+
git://git.exim.org / exim.git / blobdiff