Support "G" modifier on numbers in ${if comparisons.

[users/heiko/exim.git] / doc / doc-txt / experimental-spec.txt

diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt
index 145fc42daa58ef348924203e40c4d1c3b80dde43..5dd6832b1f6382cc71aa32f4f0736e99d5a161e8 100644 (file)
--- a/doc/doc-txt/experimental-spec.txt
+++ b/doc/doc-txt/experimental-spec.txt
@@ -1,14 +1,72 @@
-$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.
 
 
 liable to incompatibile change.
 
 

-1. Brighmail AntiSpam (BMI) suppport
+OCSP Stapling support
+--------------------------------------------------------------
+
+X509 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 one new 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.
+
+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.  There is no client support
+for OCSP in Exim, this is feature expected to be used by mail clients.
+
+
+
+
+Brightmail AntiSpam (BMI) suppport

 --------------------------------------------------------------
 
 Brightmail  AntiSpam  is  a  commercial  package.  Please  see
 --------------------------------------------------------------
 
 Brightmail  AntiSpam  is  a  commercial  package.  Please  see


@@ -32,14 +90,14 @@ instead  of per-message.  To use  BMI, you  need to  take the
 following steps:
 
   1) Compile Exim with BMI support
 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.
 
   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
 
 
 1) Adding support for BMI at compile time
 


@@ -51,16 +109,16 @@ These four steps are explained in more details below.
   with  these lines in Local/Makefile:
 
   EXPERIMENTAL_BRIGHTMAIL=yes
   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
   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.
   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"
   You    should     also    include     the    location     of
   libbmiclient_single.so in your dynamic linker  configuration
   file   (usually   /etc/ld.so.conf)   and   run    "ldconfig"


@@ -68,22 +126,22 @@ These four steps are explained in more details below.
   able to find the library file.
 
 
   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:
   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
   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.
   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
 
 
 3) Set up ACL control statement
 


@@ -95,8 +153,8 @@ These four steps are explained in more details below.
   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
   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
 
   accept  domains       = +local_domains
           endpass


@@ -107,7 +165,7 @@ These four steps are explained in more details below.
           endpass
           verify        = recipient
           control       = bmi_run
           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.
 
   If bmi_run  is not  set in  any ACL  during reception of the
   message, it will NOT be passed to the BMI server.
 


@@ -118,108 +176,108 @@ These four steps are explained in more details below.
   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
   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:
   following outcomes:

-  
+

   o deliver the message normally
   o deliver the message to an alternate location
   o do not deliver the message
   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:
   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:
   - 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
     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.
       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
     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.
       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
     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:
       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:
         # 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.
       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:
   - 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
       # 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:
   - 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
     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:
       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
       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.
       If there is no verdict available for the recipient being
       routed, this variable contains the empty string.

-    
+

     o $bmi_base64_tracker_verdict
     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:
       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
       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.
       If there is no verdict available for the recipient being
       routed, this variable contains the empty string.

-      
+

     o $bmi_alt_location
     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
       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


@@ -228,17 +286,17 @@ These four steps are explained in more details below.
       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.
       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
     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.
       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.
       $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:
   IMPORTANT NOTE: Verdict inheritance.
   The  message  is passed  to  the BMI  server  during message
   reception,  using the  target addresses  from the  RCPT TO:


@@ -247,8 +305,8 @@ These four steps are explained in more details below.
   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.
   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
 5) Using per-recipient opt-in information (Optional)
 
   The  BMI server  features multiple  scanning "profiles"  for


@@ -256,7 +314,7 @@ These four steps are explained in more details below.
   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
   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
   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


@@ -268,49 +326,49 @@ These four steps are explained in more details below.
   flag. Here is an example that will pull opt-in data for each
   recipient      from       a      flat       file      called
   '/etc/exim/bmi_optin_data'.
   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:
   The file format:

-  
+

     user1@mydomain.com: <OPTIN STRING1>:<OPTIN STRING2>
     user2@thatdomain.com: <OPTIN STRING3>
     user1@mydomain.com: <OPTIN STRING1>:<OPTIN STRING2>
     user2@thatdomain.com: <OPTIN STRING3>

-    
-    
+
+

   The example:
   The example:

-  
+

     accept  domains       = +relay_to_domains
             endpass
             verify        = recipient
             bmi_optin     = ${lookup{$local_part@$domain}lsearch{/etc/exim/bmi_optin_data}}
     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
   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.
   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.
   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.
 
 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/
 
   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 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
 Local/Makefile:
 
 EXPERIMENTAL_SPF=yes


@@ -350,9 +408,9 @@ which the spf condition should succeed. Valid strings are:
               record of the queried domain. This should be
               treated like "none".
   o err_temp  This indicates a temporary error during all
               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 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
 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


@@ -361,11 +419,12 @@ the SPF check, the condition  succeeds. If none of the  listed
 strings matches the  outcome of the  SPF check, the  condition
 fails.
 
 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
 --------------------- */
 
      spf = fail
 --------------------- */
 


@@ -391,29 +450,63 @@ variables.
   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.
   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
   $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.
   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_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".
   $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
 --------------------------------------------------------------
 
 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
 library is 0.5.
 
 In order to  use SRS, you  must get a  copy of libsrs_alt from


@@ -428,6 +521,60 @@ EXPERIMENTAL_SRS=yes
 in your Local/Makefile.
 
 
 in your Local/Makefile.
 
 

+DCC Support
+--------------------------------------------------------------
+
+*) Building exim
+
+In order to build exim with DCC support add
+
+EXPERIMENTAL_DCC=yes
+
+to your Makefile. (Re-)build/install exim. exim -d should show
+EXPERIMENTAL_DCC under "Support for".
+
+
+*) Configuration
+
+In the main section of exim.cf add at least
+  dccifd_address = /usr/local/dcc/var/dccifd
+or
+  dccifd_address = <ip> <port>
+
+In the DATA ACL you can use the new condition
+        dcc = *
+
+After that "$dcc_header" contains the X-DCC-Header.
+
+Returnvalues are:
+  fail    for overall "R", "G" from dccifd
+  defer   for overall "T" from dccifd
+  accept  for overall "A", "S" from dccifd
+
+dcc = */defer_ok works as for spamd.
+
+The "$dcc_result" variable contains the overall result from DCC
+answer.  There will an X-DCC: header added to the mail.
+
+Usually you'll use
+  defer   !dcc = *
+to greylist with DCC.
+
+If you set, in the main section,
+  dcc_direct_add_header = true
+then the dcc header will be added "in deep" and if the spool
+file was already written it gets removed. This forces Exim to
+write it again if needed.  This helps to get the DCC Header
+through to eg. SpamAssassin.
+
+If you want to pass even more headers in the middle of the
+DATA stage you can set
+  $acl_m_dcc_add_header
+to tell the DCC routines add more information; eg, you might set
+this to some results from ClamAV.  Be careful.  Header syntax is
+not checked and is added "as is".
+
+

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