SMailCallbackContext.setPreparedMessageHookOnThread(notificationHelper::send);
                CrawlerPostcard.droppedInto(postbox, postcard -> {
                    postcard.setFrom(fessConfig.getMailFromAddress(), fessConfig.getMailFromName());
                    postcard.addReplyTo(fessConfig.getMailReturnPath());
                    if (toAddresses.length > 0) {

     * The value is, e.g. root@localhost <br>
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getMailFromAddress();

    /**
     * Get the value for the key 'mail.hostname'. <br>
     * The value is, e.g.  <br>
     * @return The value of found property. (NotNull: if not found, exception but basically no way)