-$Cambridge: exim/doc/doc-txt/experimental-spec.txt,v 1.1 2005/01/11 10:51:15 ph10 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
+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.
-1. Brighmail AntiSpam (BMI) suppport
+Brightmail AntiSpam (BMI) suppport
--------------------------------------------------------------
Brightmail AntiSpam is a commercial package. Please see
following steps:
1) Compile Exim with BMI support
- 2) Set up main BMI options (top section of exim config file)
+ 2) Set up main BMI options (top section of Exim config file)
3) Set up ACL control statement (ACL section of the config
file)
4) Set up your routers to use BMI verdicts (routers section
of the config file).
5) (Optional) Set up per-recipient opt-in information.
-These four steps are explained in more details below.
+These four steps are explained in more details below.
1) Adding support for BMI at compile time
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
merge the content of these lines with them.
Note for BMI6.x users: You'll also have to add -lxml2_single
to the EXTRALIBS_EXIM line. Users of 5.5x do not need to do
this.
-
+
You should also include the location of
libbmiclient_single.so in your dynamic linker configuration
file (usually /etc/ld.so.conf) and run "ldconfig"
able to find the library file.
-2) Setting up BMI support in the exim main configuration
+2) Setting up BMI support in the Exim main configuration
- To enable BMI support in the main exim configuration, you
+ To enable BMI support in the main Exim configuration, you
should set the path to the main BMI configuration file with
the "bmi_config_file" option, like this:
-
+
bmi_config_file = /opt/brightmail/etc/brightmail.cfg
-
- This must go into section 1 of exims configuration file (You
+
+ This must go into section 1 of Exim's configuration file (You
can put it right on top). If you omit this option, it
defaults to /opt/brightmail/etc/brightmail.cfg.
Note for BMI6.x users: This file is in XML format in V6.xx
and its name is /opt/brightmail/etc/bmiconfig.xml. So BMI
6.x users MUST set the bmi_config_file option.
-
+
3) Set up ACL control statement
an "accept" block in the "acl_check_rcpt" ACL. You should
use the "accept" block(s) that accept messages from remote
servers for your own domain(s). Here is an example that uses
- the "accept" blocks from exims default configuration file:
-
+ the "accept" blocks from Exim's default configuration file:
+
accept domains = +local_domains
endpass
endpass
verify = recipient
control = bmi_run
-
+
If bmi_run is not set in any ACL during reception of the
message, it will NOT be passed to the BMI server.
more "verdicts" are present. Different recipients can have
different verdicts. Each recipient is treated individually
during routing, so you can query the verdicts by recipient
- at that stage. From Exims view, a verdict can have the
+ at that stage. From Exim's view, a verdict can have the
following outcomes:
-
+
o deliver the message normally
o deliver the message to an alternate location
o do not deliver the message
-
+
To query the verdict for a recipient, the implementation
offers the following tools:
-
-
+
+
- Boolean router preconditions. These can be used in any
router. For a simple implementation of BMI, these may be
all that you need. The following preconditions are
available:
-
+
o bmi_deliver_default
-
+
This precondition is TRUE if the verdict for the
recipient is to deliver the message normally. If the
message has not been processed by the BMI server, this
variable defaults to TRUE.
-
+
o bmi_deliver_alternate
-
+
This precondition is TRUE if the verdict for the
recipient is to deliver the message to an alternate
location. You can get the location string from the
$bmi_alt_location expansion variable if you need it. See
further below. If the message has not been processed by
the BMI server, this variable defaults to FALSE.
-
+
o bmi_dont_deliver
-
+
This precondition is TRUE if the verdict for the
recipient is NOT to deliver the message to the
recipient. You will typically use this precondition in a
top-level blackhole router, like this:
-
+
# don't deliver messages handled by the BMI server
bmi_blackhole:
driver = redirect
bmi_dont_deliver
data = :blackhole:
-
+
This router should be on top of all others, so messages
that should not be delivered do not reach other routers
at all. If the message has not been processed by
the BMI server, this variable defaults to FALSE.
-
-
+
+
- A list router precondition to query if rules "fired" on
the message for the recipient. Its name is "bmi_rule". You
use it by passing it a colon-separated list of rule
numbers. You can use this condition to route messages that
matched specific rules. Here is an example:
-
+
# special router for BMI rule #5, #8 and #11
bmi_rule_redirect:
driver = redirect
bmi_rule = 5:8:11
data = postmaster@mydomain.com
-
-
+
+
- Expansion variables. Several expansion variables are set
during routing. You can use them in custom router
conditions, for example. The following variables are
available:
-
+
o $bmi_base64_verdict
-
+
This variable will contain the BASE64 encoded verdict
for the recipient being routed. You can use it to add a
header to messages for tracking purposes, for example:
-
+
localuser:
driver = accept
check_local_user
headers_add = X-Brightmail-Verdict: $bmi_base64_verdict
transport = local_delivery
-
+
If there is no verdict available for the recipient being
routed, this variable contains the empty string.
-
+
o $bmi_base64_tracker_verdict
-
+
This variable will contain a BASE64 encoded subset of
the verdict information concerning the "rules" that
fired on the message. You can add this string to a
header, commonly named "X-Brightmail-Tracker". Example:
-
+
localuser:
driver = accept
check_local_user
headers_add = X-Brightmail-Tracker: $bmi_base64_tracker_verdict
transport = local_delivery
-
+
If there is no verdict available for the recipient being
routed, this variable contains the empty string.
-
+
o $bmi_alt_location
-
+
If the verdict is to redirect the message to an
alternate location, this variable will contain the
alternate location string returned by the BMI server. In
there is no verdict available for the recipient being
routed, or if the message is to be delivered normally,
this variable contains the empty string.
-
+
o $bmi_deliver
-
+
This is an additional integer variable that can be used
to query if the message should be delivered at all. You
should use router preconditions instead if possible.
-
+
$bmi_deliver is '0': the message should NOT be delivered.
$bmi_deliver is '1': the message should be delivered.
-
-
+
+
IMPORTANT NOTE: Verdict inheritance.
The message is passed to the BMI server during message
reception, using the target addresses from the RCPT TO:
inherit the verdict from the original address. This means
that verdicts also apply to all "child" addresses generated
from top-level addresses that were sent to the BMI server.
-
-
+
+
5) Using per-recipient opt-in information (Optional)
The BMI server features multiple scanning "profiles" for
server and are queried by the BMI server itself. However,
you can also pass opt-in data for each recipient from the
MTA to the BMI server. This is particularly useful if you
- already look up recipient data in exim anyway (which can
+ already look up recipient data in Exim anyway (which can
also be stored in a SQL database or other source). This
implementation enables you to pass opt-in data to the BMI
server in the RCPT ACL. This works by setting the
flag. Here is an example that will pull opt-in data for each
recipient from a flat file called
'/etc/exim/bmi_optin_data'.
-
+
The file format:
-
+
user1@mydomain.com: <OPTIN STRING1>:<OPTIN STRING2>
user2@thatdomain.com: <OPTIN STRING3>
-
-
+
+
The example:
-
+
accept domains = +relay_to_domains
endpass
verify = recipient
bmi_optin = ${lookup{$local_part@$domain}lsearch{/etc/exim/bmi_optin_data}}
- control = bmi_run
-
+ control = bmi_run
+
Of course, you can also use any other lookup method that
- exim supports, including LDAP, Postgres, MySQL, Oracle etc.,
+ Exim supports, including LDAP, Postgres, MySQL, Oracle etc.,
as long as the result is a list of colon-separated opt-in
strings.
-
+
For a list of available opt-in strings, please contact your
Brightmail representative.
-
-
-
-2. Sender Policy Framework (SPF) support
+
+
+
+Sender Policy Framework (SPF) support
--------------------------------------------------------------
-To learn more about SPF, visit http://spf.pobox.com. This
+To learn more about SPF, visit http://www.openspf.org. 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
+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
+To compile Exim with SPF support, set these additional flags in
Local/Makefile:
EXPERIMENTAL_SPF=yes
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.
+ 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
strings matches the outcome of the SPF check, the condition
fails.
-Here is a simple example to fail forgery attempts from domains
-that publish SPF records:
+Here is an example to fail forgery attempts from domains that
+publish SPF records:
/* -----------------
-deny message = $sender_host_address is not allowed to send mail from $sender_address_domain
+deny message = $sender_host_address is not allowed to send mail from ${if def:sender_address_domain {$sender_address_domain}{$sender_helo_name}}. \
+ Please see http://www.openspf.org/Why?scope=${if def:sender_address_domain {mfrom}{helo}};identity=${if def:sender_address_domain {$sender_address}{$sender_helo_name}};ip=$sender_host_address
spf = fail
--------------------- */
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
+ This contains a complete Received-SPF: 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.
-
+
+ Note: in case of "Best-guess" (see below), the convention is
+ to put this string in a header called X-SPF-Guess: instead.
+
$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.
-
+
$spf_smtp_comment
This contains a string that can be used in a SMTP response
to the calling party. Useful for "fail".
-
-
-3. SRS (Sender Rewriting Scheme) Support
+In addition to SPF, you can also perform checks for so-called
+"Best-guess". Strictly speaking, "Best-guess" is not standard
+SPF, but it is supported by the same framework that enables SPF
+capability. Refer to http://www.openspf.org/FAQ/Best_guess_record
+for a description of what it means.
+
+To access this feature, simply use the spf_guess condition in place
+of the spf one. For example:
+
+/* -----------------
+deny message = $sender_host_address doesn't look trustworthy to me
+ spf_guess = fail
+--------------------- */
+
+In case you decide to reject messages based on this check, you
+should note that although it uses the same framework, "Best-guess"
+is NOT SPF, and therefore you should not mention SPF at all in your
+reject message.
+
+When the spf_guess condition has run, it sets up the same expansion
+variables as when spf condition is run, described above.
+
+Additionally, since Best-guess is not standarized, you may redefine
+what "Best-guess" means to you by redefining spf_guess variable in
+global config. For example, the following:
+
+/* -----------------
+spf_guess = v=spf1 a/16 mx/16 ptr ?all
+--------------------- */
+
+would relax host matching rules to a broader network range.
+
+
+SRS (Sender Rewriting Scheme) Support
--------------------------------------------------------------
Exiscan currently includes SRS support via Miles Wilton's
-libsrs_alt library. The current version of the supported
+libsrs_alt library. The current version of the supported
library is 0.5.
In order to use SRS, you must get a copy of libsrs_alt from
git://git.exim.org / exim.git / blobdiff