http://undeadly.org/cgi?action=article&sid=20130130081741

void
mail_cb(uint64_t id, struct filter_mail *p, void *arg)
{
    /* block idiots */
    if (! strcmp(p->domain, "0pointer.net")) {
        filter_api_reject(id, 530, "You're not welcome, go away !");
        return;
    }

    filter_api_accept(id);
}

// тонко