Hi everybody.
I need your help to solve this issue. I presume some parameter must be configure on my server in order to avoid this kind of situation.
I will try to explain in the best possible manner the problem that I am experimenting.

Somebody out there [not me or any of email accounts hosted on my server of course] is using my email account name to send spam to my email account.

Regards.
Francisco.

My server has the following versions:

cPanel 11.25.0-R46156 - WHM 11.25.0 - X 3.9
REDHAT Enterprise 4 x86_64 standard


Internet headers that I got from one of this email message:

Return-path: <fjgaston@siccv.com.mx>
Envelope-to: fjgaston@siccv.com.mx
Delivery-date: Tue, 29 Jun 2010 12:04:02 -0500
Received: from [188.51.1.56] (helo=[188.50.57.147])
by mxsrv001tx.siccv.com.mx with esmtp (Exim 4.69)
(envelope-from <fjgaston@siccv.com.mx>)
id 1OTeE1-0004Cz-Cp
for fjgaston@siccv.com.mx; Tue, 29 Jun 2010 12:03:57 -0500
From: <fjgaston@siccv.com.mx>
To: fjgaston@siccv.com.mx
Date: Tue, 29 Jun 2010 20:03:56 +0300
Subject: {Spam?} Hot Sale on Viagra
Reply-To: <fjgaston@siccv.com.mx>
MIME-Version: 1.0
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 8bit
X-HostingServicesSiCCV-MailScanner-Information: Please contact the ISP for more information
X-HostingServicesSiCCV-MailScanner-ID: 1OTeE1-0004Cz-Cp
X-HostingServicesSiCCV-MailScanner: Found to be clean
X-HostingServicesSiCCV-MailScanner-SpamCheck: spam,
SpamAssassin (score=18.931, required 5, autolearn=spam,
BAYES_99 5.00, DRUGS_ERECTILE 0.28, FH_DATE_PAST_20XX 3.19,
MISSING_MID 0.00, RAZOR2_CF_RANGE_51_100 0.50,
RAZOR2_CF_RANGE_E8_51_100 1.50, RAZOR2_CHECK 0.50, RCVD_IN_PBL 0.91,
RDNS_NONE 0.10, URIBL_BLACK 1.96, URIBL_SBL 5.00)
X-HostingServicesSiCCV-MailScanner-SpamScore: ssssssssssssssssss
X-HostingServicesSiCCV-MailScanner-From: fjgaston@siccv.com.mx