Integrated SPF Best Guess. Fixes: bug #521

[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 cff937f7fb0815d69bd43c5bf0a1a3c8d999b70e..4175173c320d5cf1113133a8dd7117807a152e54 100644 (file)
--- a/doc/doc-txt/experimental-spec.txt
+++ b/doc/doc-txt/experimental-spec.txt
@@ -1,4 +1,4 @@
-$Cambridge: exim/doc/doc-txt/experimental-spec.txt,v 1.9 2007/10/04 13:21:06 tom Exp $
+$Cambridge: exim/doc/doc-txt/experimental-spec.txt,v 1.11 2008/02/12 12:52:51 nm4 Exp $
 
 From time to time, experimental features may be added to Exim.
 While a feature  is experimental, there  will be a  build-time
@@ -697,7 +697,7 @@ These four steps are explained in more details below.
 3. 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.
@@ -761,11 +761,12 @@ the SPF check, the condition  succeeds. If none of the  listed
 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
 --------------------- */
 
@@ -798,6 +799,9 @@ variables.
   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
@@ -807,6 +811,37 @@ variables.
   This contains a string that can be used in a SMTP response
   to the calling party. Useful for "fail".
 
+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.
 
 
 4. SRS (Sender Rewriting Scheme) Support