Re: Group Auto-Email Module - German lang, spam problem

Hello,

Thanks for this mod, it works fine!

Here are the German language files:
german-sie.php:

<?php
$PHORUM["DATA"]["LANG"]["group_sub"]["NewMessage"] = "Thema:\n%subject%\n\nBeitrag:\n%plain_body%\n\nSehen Sie den gesamten Diskussionsstrang:\n%read_url%";
$PHORUM["DATA"]["LANG"]["group_sub"]["NewMessageSubject"] = "Neuer Beitrag in %forumname%";
?>

german-du-female.php and german-du-male.php:

<?php
$PHORUM["DATA"]["LANG"]["group_sub"]["NewMessage"] = "Thema:\n%subject%\n\nBeitrag:\n%plain_body%\n\nSiehe den gesamten Diskussionsstrang:\n%read_url%";
$PHORUM["DATA"]["LANG"]["group_sub"]["NewMessageSubject"] = "Neuer Beitrag in %forumname%";
?>

But there is a problem regarding to spam.
Since having installed Phorum 5.1.25 as a non-public forum (read-access only for registered users!) including the group auto-email mod, we - and all of our users! - get spam characterized by the following:
From is only -
Subject is empty
Body is empty, too
Header (= source code) is like the following (I have changed the mail address, IP, domain and user names):

From - Wed Dec 12 15:15:22 2007
X-UIDL: 1197468211.6746.mail4.ourreceivingmailserver.net,S=480
X-Mozilla-Status: 0001
X-Mozilla-Status2: 00000000
Return-Path: <ud00_000@mail.ourwebhostingprovider.de>
Delivered-To: me@example.com
Received: (qmail 6743 invoked by uid 89); 12 Dec 2007 14:03:31 -0000
Received: by simscan 1.3.1 ppid: 2349, pid: 2367, t: 120.4306s
scanners: attach: 1.3.1 clamav: 0.91.1/m:
Received: from unknown (HELO mail.ourwebhostingprovider.de) (194.000.000.00)
by 0 with SMTP; 12 Dec 2007 14:03:31 -0000
Received-SPF: none (0: domain at mail.ourwebhostingprovider.de does not designate permitted sender hosts)

How this can happen in a non-public forum? Is this a matter of the module? What can we do to protect our users from this spam? Thanks for advice!