function rbl_lookup($ipv4) {
    $ip = explode(".", $ipv4);
    $rbl_url = ".rbl.blockedservers.com";
    $rbl_hostname = $ip[3].".".$ip[2].".
                  ".$ip[1].".".$ip[0]."". $rbl_url;

    $rbl_lookup = gethostbyname($rbl_hostname);

    if($rbl_lookup == $rbl_hostname) {
        return 1;
    }
    else {
        return 0;
    }
}

#!/usr/bin/perl
# ./api_perl.pl 123.234.123.234

use Net::DNS;

$check_host = join(".", reverse(split(/\./, $ARGV[0]))) .
                 '.rbl.blockedservers.com';
$check_data = Net::DNS::Resolver->new;
$check_query = $check_data->search("$check_host");

if($check_query) {
    print "$ARGV[0] is listed.\n";
}
else {
    print "$ARGV[0] is not listed.\n";
}

#
# Main.cf
#

smtpd_client_restrictions = permit_mynetworks,
        permit_sasl_authenticated,
        reject_unauth_destination,
        reject_rbl_client rbl.blockedservers.com,
        permit

@dnsbl_score = (
  "pbl.spamhaus.org",     3.25,   0,      "DYN_PBL_SPAMHAUS",
  "dnsbl.njabl.org",      4.25,   -1.5,   "BL_NJABL",
  "bl.spamcop.net",       1.75,   -1.5,   "SPAMCOP",
  "sbl-xbl.spamhaus.org", 4.35,   -1.5,   "SBL_XBL_SPAMHAUS",
  "list.dsbl.org",        4.35,   0,      "DSBL_ORG",
  "ix.dnsbl.manitu.net",  4.35,   0,      "IX_MANITU",
  "relays.ordb.org",      3.25,   0,      "ORDB_ORG",
  "rbl.blockedservers.com", 1.25,   0,    "BLOCKEDSERVERS_COM"
);