Qmail bounce message contains multiple addresses

[Eck!]

Hi, can anyone shed any light on this message. Basically, I sent an email out which appears to have bounced, but the bounce message contains failure notices for several other addresses which appear to have tagged onto the original message. Ive changed the addresses, but basically I dont recognise any of these addresses and I certainly didnt send them this message. The intended recipient is not in the list of failures so I guess they received the message OK.

Any advice welcome as Im now worried my server is being used for spamming (I have all the usual security patches in place but I did discover a compromised customer account a few weeks ago which has now been closed)

Heres the bounce message I received...

Hi. This is the qmail-send program at XXXXXXXXXXXXX.
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.

<p2jcp2@XXXX.net>:
216.33.127.00 failed after I sent the message.
Remote host said: 550 5.2.0 c9c91d01w2MKksX049c91X Message identified as SPAM

<p2d1c1@YYYY.net>:
207.109.18.00 does not like recipient.
Remote host said: 550 5.1.1 <p2d1c1@qwest.net>: Recipient address rejected: User unknown
Giving up on 207.109.18.195.

<p47siebel@XXXX.net>:
216.33.127.00 failed after I sent the message.
Remote host said: 550 5.2.0 c9cp1d01J2MKksX049cpfC Message identified as SPAM - 

<p511@XXXX.net>:
216.33.127.00 does not like recipient.
Remote host said: 550 5.1.1 c9cv1d0222MKksX049cv91 Invalid recipient: <p511@XXXX.net> E3210
Giving up on 216.33.127.20.

<p5111@XXXX.net>:
216.33.127.00 does not like recipient.
Remote host said: 550 5.1.1 c9cv1d02a2MKksX049cvDU Invalid recipient: <p5111@XXXX.net> E3210
Giving up on 216.33.127.20.

<ZZZZ@aol.coom>:
Sorry, I couldn't find any host named aol.coom. (#5.1.2)

<p3jk4moe@ZZZZ.net>:
216.135.0.00 does not like recipient.
Remote host said: 550 unknown user <p3jk4moe@owensboro.net> (rtr sam.ZZZZ.net 0x1C)
Giving up on 216.135.0.187.

<pa105@WWWW.edu>:
128.59.48.00 failed after I sent the message.
Remote host said: 554 5.7.1 This message appears to be unsolicited bulk mail

<pa.gr.sitz@VVVV.org>:
140.98.193.00 failed after I sent the message.
Remote host said: 554 5.7.1 Message rejected because of unacceptable content.  For help, please quote incident ID 75948901.

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

Return-Path: <reply@MYDOMAIN.net>
Received: (qmail 25214 invoked by uid 48); 25 Feb 2010 11:28:48 +0000
To: export@THE_REAL_ADDRESS.be
Subject: Book Fair - 23-26 March
Date: Thu, 25 Feb 2010 11:28:48 +0000
From: ME <me@mydomain.com>
Message-ID: <25a7d25c9be629156d1d53ed47f1636a@cp.mydomain.net>
X-Priority: 3
MIME-Version: 1.0
Content-Type: multipart/alternative;
boundary="b1_25a7d25c9be629156d1d53ed47f1636a"