spam mail in qmail queue

[socalheel]

I routinely notice multiple spam messages in the qmail queue and I don't know how to track how they are originating. Can someone give guidance?

Here is an example:

Received: (qmail 5897 invoked for bounce); 26 Apr 2014 11:02:21 -0400
Date: 26 Apr 2014 11:02:21 -0400
From: MAILER-DAEMON@myserver.net
To: forum@hosted.website.org
Subject: failure notice

Hi. This is the qmail-send program at myserver.net.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

<kyhqy2de@isac-hermes.com>:
MY IP ADDRESS failed after I sent the message.
Remote host said: 550-5.7.1 [12.12.12.12      12] Our system has detected that this message is
550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to Gmail,
550-5.7.1 this message has been blocked. Please visit
550-5.7.1 http://support.google.com/mail/bin/answer.py?hl=en&answer=188131 for
550 5.7.1 more information. w93si5471915qge.76 - gsmtp

--- Below this line is a copy of the message.

Return-Path: <forum@hosted.website.org>
Received: (qmail 5006 invoked by uid 48); 26 Apr 2014 11:01:49 -0400
To: kyhqy2de@isac-hermes.com
Subject: Welcome to Hosted Website Forums
Reply-to: forum@hosted.website.org
From: forum@hosted.website.org
Message-ID: <e13107642f2c23b99f951047061ad19e@forum.hosted.website.org>
MIME-Version: 1.0
Content-type: text/plain; charset=iso-8859-1
Content-transfer-encoding: 8bit
Date: Sat, 26 Apr 2014 11:01:49 -0400
X-Priority: 3
X-MSMail-Priority: Normal
X-Mailer: PHP
X-MimeOLE: Produced By <forum software version>

Welcome to Hosted Website Forums

Please keep this email for your records. Your account information is as follows:

----------------------------
Username: <fake name>
Password: <faked password>
----------------------------

Your account is currently inactive, the administrator of the board will need to activate it before you can log in. You will receive another email when this has occured.

Please do not forget your password as it has been encrypted in our database and we cannot retrieve it for you. However, should you forget your password you can request a new one which will be activated in the same way as this account.

Thank you for registering.

-- 
Thanks, 
Forum Administrator
forum@hosted.website.org