If you are using Windows server 2008 SBS or Exchange 2007 or Exchange 2010 you send with your e-mail also mail headers that (I think) you would not like to “share” with external world:

Received: from mail.server.si (xxx.xxx.xxx.xxx) by mail.server2.si
 (172.31.200.2) with Microsoft SMTP Server (TLS) id 8.2.247.2; Wed, 19 May
 2010 13:08:47 +0200
Received: from SRVEXCH01.domain.local ([10.11.12.2]) by SRVEXCH01.domain.local
 ([10.11.12.2]) with mapi; Wed, 19 May 2010 13:08:02 +0200
From: xxxxx xxxxx xxxxx@xxxxx
To: =?iso-8859-2?Q?xxxxx_xxxxx=E6_=28xxxxx=xxxxx=2Exxxxx=29?=
 <xxxxx@xxxxx>
Return-Receipt-To: xxxxx@xxxxx
Date: Wed, 19 May 2010 13:08:00 +0200
Subject: xxxxx
Thread-Topic: xxxxx
Thread-Index: Acr3Q4r6dSBNnU37R9ypBLYy8PMzcA==
Message-ID: <13204AAD07BCDD4EB69C3367FF1783A9124C065BB2@SRVEXCH01.domain.local>
Accept-Language: sl-SI
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
acceptlanguage: sl-SI
Content-Type: multipart/alternative;
 boundary=”_000_13204AAD07BCDD4EB69C3367FF1783A9124C065BB2_”
MIME-Version: 1.0
Return-Path: xxxxx@xxxxx
X-MS-Exchange-Organization-PRD: xxxxx.si
X-MS-Exchange-Organization-SenderIdResult: Pass
Received-SPF: Pass (xxxxx.xxxxx.xxxxx: domain of xxxxx@xxxxx
 designates xxx.xxx.xxx.xxx as permitted sender) receiver=xxxxx.xxxxx.local;
 client-ip=xxx.xxx.xxx.xxx; helo=mail.xxxxx.si;
X-MS-Exchange-Organization-SCL: 1
X-MS-Exchange-Organization-PCL: 2
X-MS-Exchange-Organization-Antispam-Report: DV:3.3.8917.498;SV:3.3.8919.449;SID:SenderIDStatus Pass;OrigIP:xxx.xxx.xxx.xxx

If you want to remove this stuff we need to create a Hub Transport Rule:
Open Microsoft Exchange Console
Navigate to:
Microsoft Exchange Organization Configuration Hub Transport Transport Rules

Right Click and select New Transport Rule and name it “Remove headers” click Next,

chose From users inside or outside the organization and select Inside click Next,chose Remove header and as message header just write: Received twice click Next…

You are done… Headers will not be sent any more to users outside the organization…

Bye,
Luka (under influence of wonderful NT Konferenca 2010)