How to prevent spam from server?

[Alexk]

Someone spammed from my server:

From [email protected] Mon Nov 19 02:42:04 2007
"
Delivered-To: x
Received: by 10.142.155.9 with SMTP id c9cs244638wfe;
Sun, 18 Nov 2007 17:42:04 -0800 (PST)
Received: by 10.140.169.4 with SMTP id r4mr1242898rve.1195436524640;
Sun, 18 Nov 2007 17:42:04 -0800 (PST)
Return-Path: <[email protected]>
Received: from s1.myserver.tld ([116.0.103.100])
by mx.google.com with SMTP id
> l32si6949428rvb.2007.11.18.17.42.03;
> Sun, 18 Nov 2007 17:42:04 -0800 (PST)
> Received-SPF: neutral (google.com: MY.IP.ADRESS.HERE is neither permitted
> nor denied by domain of [email protected]) client-ip=MY.IP.ADRESS.HERE;
> Authentication-Results: mx.google.com; spf=neutral (google.com:
> MY.IP.ADRESS.HERE is neither permitted nor denied by domain of
> [email protected]) [email protected]
> Received: from fkdc (55.236.97.1)
> by s1.myserver.tld; Mon, 19 Nov 2007 04:42:19 +0300
> Date: Mon, 19 Nov 2007 04:42:19 +0300
> From: <[email protected]>
> X-Mailer: The Bat! (v2.01)
> Reply-To: <[email protected]>
> X-Priority: 3 (Normal)
> Message-ID: <[email protected]>
> To: <x>
> Subject: Up to 2.27% Daily ~ tMJo
> MIME-Version: 1.0
> Content-Type: multipart/mixed;
> boundary="----------F028CB65C45E9B"
>
> ------------F028CB65C45E9B
> Content-Type: text/html; charset=windows-1251
> Content-Transfer-Encoding: 8bit
>
>
> 4
> ------------F028CB65C45E9B--

In /exim/mainlog I just can see:

2007-11-19 03:32:30 1ItuYw-0005lg-MM <= [email protected] H=localhost (s1.myserver.tld) [127.0.0.1] P=smtp S=1469 [email protected] T="Up to 2.27% Daily ~ vai" from <[email protected]> for [email protected]


How I can find out who is spammer and how I can prevent it?

Thanks.