Example Perl greylist server

This is the Perl subroutine that implements the example greylist policy. It is part of a general purpose sample policy server that is distributed with the Postfix source as examples/smtpd-policy/greylist.pl.

#
# greylist status database and greylist time interval. DO NOT create the
# greylist status database in a world-writable directory such as /tmp
# or /var/tmp. DO NOT create the greylist database in a file system
# that can run out of space.
#
$database_name="/var/mta/greylist.db";
$greylist_delay=60;

#
# Demo SMTPD access policy routine. The result is an action just like
# it would be specified on the right-hand side of a Postfix access
# table.  Request attributes are available via the %attr hash.
#
sub smtpd_access_policy {
    my($key, $time_stamp, $now);

    # Open the database on the fly.
    open_database() unless $database_obj;

    # Lookup the time stamp for this client/sender/recipient.
    $key =
        lc $attr{"client_address"}."/".$attr{"sender"}."/".$attr{"recipient"};
    $time_stamp = read_database($key);
    $now = time();

    # If new request, add this client/sender/recipient to the database.
    if ($time_stamp == 0) {
        $time_stamp = $now;
        update_database($key, $time_stamp);
    }

    # The result can be any action that is allowed in a Postfix 
access(5) map.
    #
    # To label the mail, return ``PREPEND headername: headertext''
    #
    # In case of success, return ``DUNNO'' instead of ``OK'', so that the
    # 
check_policy_service restriction can be followed by other restrictions.
    #
    # In case of failure, return ``DEFER_IF_PERMIT optional text...'',
    # so that mail can still be blocked by other access restrictions.
    #
    syslog $syslog_priority, "request age %d", $now - $time_stamp if $verbose;
    if ($now - $time_stamp > $greylist_delay) {
        return "dunno";
    } else {
        return "
defer_if_permit Service temporarily unavailable";
    }
}