[Pkg-exim4-users] Problems with spam

[Steven Lobbezoo]

Hi,

Since many years now I use exim (now 4) on my server at complete
satisfaction.

However, now i'm getting problems with spammers, not a fault of exim,
and i donnot know how to handle them.

Some spammers use an e-mail addres from my system to send spam all over
the world.
The header looks like this :

Received: from 78.56.135.86 ([78.56.135.86]) by alojamientowindows.net
with MailEnable ESMTP; Tue, 13 May 2008 17:40:22 -0500
Message-ID: <000801c8b54a$04445066$612e18b1 at qpflitn>
From: "S0MA is your reliable pain relief." <webmaster at la-france.net>
To: <ventas at regalandoflores.com>
Subject: Revolution in the PE science
Date: Tue, 13 May 2008 20:52:57 +0000
MIME-Version: 1.0
Content-Type: multipart/related;
        type="multipart/alternative";
        boundary="----=_NextPart_000_0003_01C8B54A.043FF9BB"
X-Priority: 3
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 6.00.2900.3138
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198

This is a multi-part message in MIME format.

------=_NextPart_000_0003_01C8B54A.043FF9BB
Content-Type: multipart/alternative;
        boundary="----=_NextPart_001_0004_01C8B54A.043FF9BB"
etc. etc.

As you can see, From adress is webmaster at la-france.net (thats me) but
the message is send from 78.56.135.86 (thats NOT me).
The result is that i'm inondated with messages from postmasters
everywhere telling me the target does not exists or that the mail was
clasified as spam.

Now, for obvious reasons, i cannot block all mail coming from
postmasters. 

Is there any solution to this problem ?

Thanks,

Steven