Emails are being sent from my default server email

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I have a powerboost shared hosting service and i use 3-4 email addresses. When system sends an email, it sends it from the default server email address which is like a catch all account.
Something like server.3322.@hostingcompany.com

Now my hosting company suspended my account saying there were huge amounts of spams are being sent from that default email address and they have attached one of them also in the notice email. But i donno what do to now.

Below is the email (including header) the hosting company sent me as an example of the spam being sent from the default server email.

I had to censor some parts for security purposes.

1RyWht-003PaS-4M-H
servername 1071 32007
<*****@slan-550-88.****.com>
1329519313 0
-ident ****
-received_protocol local
-body_linecount 740
-max_received_linelength 86
-auth_id ******@slan-550-88.***.com
-allow_unqualified_recipient
-allow_unqualified_sender
-local
XX
1
REMOVED

215P Received: from *** by slan-550-88.***.com with local (Exim 4.69)
(envelope-from <***@slan-550-88.***.com>)
id 1RyWht-003PaS-4M
for [email]REMOVED]; Fri, 17 Feb 2012 15:55:13 -0700
030T To: REMOVED
034 Subject: Track your parcel NO1162
048F From: "FedEx Service" <international@fedex.com>
028 X-Mailer: Bjjniad(ver.74.9)
052R Reply-To: "FedEx Service" <international@fedex.com>
018 Mime-Version: 1.0
074 Content-Type:multipart/mixed;boundary="----------13295193134F3EDAD111C7B"
058I Message-Id: <E1RyWht-003PaS-4M@slan-550-88.***.com>
038 Date: Fri, 17 Feb 2012 15:55:13 -0700


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