[exim] Understanding DomainKeys

I'm having problems with my domainkeys passing on some mail servers
(Yahoo!) and failing on others. I've got someone trying to help me a
bit, he says to check the function that's being called. It might be
older perl module that had some problems. I'm trying to understand what
function is called. Below is some excerpts from my exim.conf file.
Then the "mailtrapheaders" function is shown below, but it doesn't seem
to add the DK headers. Any way to help me figure out what's being called?

Do I need to know how exim was compiled? I'm using cpanel, so I don't
really handle the compiling of the programs. If I do need to know, is
there a way to have exim export its compile settings?

thanks,
terry

dk_lookuphost:
    driver = dnslookup
    domains = ! +local_domains
    #ignore verisign to prevent waste of bandwidth
    ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8 : 64.94.110.0/24
    require_files = 
"/var/cpanel/domain_keys/private/${sender_address_domain}"
    headers_add = "${perl{mailtrapheaders}}"
    transport = dk_remote_smtp

dk_remote_smtp:
driver = smtp
dk_private_key = "/var/cpanel/domain_keys/private/${dk_domain}"
dk_selector = default


PERL EXCERPT
sub mailtrapheaders {
my $primary_hostname = Exim::expand_string('$primary_hostname');
my $original_domain = Exim::expand_string('$original_domain');
my $sender_address_domain =
Exim::expand_string('$sender_address_domain');
my $originator_uid = Exim::expand_string('$originator_uid');
my $originator_gid = Exim::expand_string('$originator_gid');
my $caller_uid = Exim::expand_string('$caller_uid');
my $caller_gid = Exim::expand_string('$caller_gid');
my $xsource = $ENV{'X-SOURCE'};
my $xsourceargs = $ENV{'X-SOURCE-ARGS'};
my $xsourcedir = maskdir($ENV{'X-SOURCE-DIR'});

   my $headers = "X-AntiAbuse: This header was added to track abuse, 
please include it with any abuse report\n"
               . "X-AntiAbuse: Primary Hostname - $primary_hostname\n"
               . "X-AntiAbuse: Original Domain - $original_domain\n"
               . "X-AntiAbuse: Originator/Caller UID/GID - 
[$originator_uid $originator_gid] / [$caller_uid $caller_gid]\n"
               . "X-AntiAbuse: Sender Address Domain - 
$sender_address_domain\n"
                . "X-Source: ${xsource}\n"
                . "X-Source-Args: ${xsourceargs}\n"
                . "X-Source-Dir: ${xsourcedir}";
   return($headers);

}