Unix Server Tech Knowledge Base

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
====== SPF and Include Directive ======

[[wp>Sender_Policy_Framework|SPF]] allows //include:// directives, but there are also limits to the number of DNS lookups which can be made. Since included rules can contain other included rules, it is not simple to determine how many levels you have, and you can quickly exceed the number of DNS lookups

[[https://tools.ietf.org/html/rfc7208#section-4.6.4|RFC 7208 (section 4.6.4)]] states

   Some mechanisms and modifiers (collectively, "terms") cause DNS
   queries at the time of evaluation, and some do not.  The following
   terms cause DNS queries: the "include", "a", "mx", "ptr", and
   "exists" mechanisms, and the "redirect" modifier.  SPF
   implementations MUST limit the total number of those terms to 10
   during SPF evaluation, to avoid unreasonable load on the DNS


The following scripts does not take all of that into account, though it could be easily modified to do so. Instead, it simply builds a visual display of the //include// tree. To get an accurate account, add the records in the RFC above, or simply visit [[http://mxtoolbox.com/]] which has some very good tools to check your spf records

Note: this was a quick and dirty, and could use some cleanup, especially since there aren't even comments in it. Requires a system with the commands //dig// and //grep// on it.


<code perl tracespf>
#! /usr/bin/env perl

use warnings;
use strict;

sub getIncludes {
   my $indent = shift;
   my $return = '';
   foreach my $domain ( @_ ) {
      $return .= ' 'x$indent . "$domain\n";
      my @lines = `dig $domain TXT | grep spf`;
      chomp @lines;
      foreach my $entry ( @lines ) {
         while ( $entry =~ m/include:([_a-zA-Z0-9\-\.]+)/g ) {
            $return .= &getIncludes( $indent+3, $1 );
         } # while
      } # foreach
   } # foreach
   return $return;
} # sub

while ( my $domain = shift ) {
   print &getIncludes( 0, $domain );
}
1;
   
</code>