postfix email header information

What I want to do is change the Message-ID to @domain.com and the received from maybe too, but mostly the Message-ID is the problem, because my emails could be getting marked as spam since it looks like the message id has been forged. I know (think) that I could change this from the sending client machines, but it seems like this should be done in postfix. When I look at other domains that send me email, their headers look much better and they dont have the Message-ID set wrong like mine.

Here is an example message ID from a message I sent to myself - I am going to change some of the information, like the actual domain name and so fourth.

Return-Path:[fred@example.com>
X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on
host.mainserverdomain.com
X-Spam-Level:
X-Spam-Status: No, score=-3.2 required=3.9 tests=ALL_TRUSTED,AWL,BAYES_00,
HTML_90_100,HTML_MESSAGE autolearn=ham version=3.1.3
X-Original-To: fred@example.com
Delivered-To: fred-example.com@host.mainserverdomain.com
Received: from daisy2 (unknown [[12.122.126.215]])
by host.mainserverdomain.com (Postfix) with ESMTP id BDADECFE53
for[fred@example.com>; Wed, 21 Mar 2007 15:50:46 -0400 (EDT)
From: "Bill Wilson"[fred@example.com>
To:[fred@example.com>
Subject: 10
Date: Wed, 21 Mar 2007 15:50:59 -0400
Message-ID:[01b101c76bf2$428e2ce0$8001a8c0@windowsdomainname.com>
MIME-Version: 1.0
Content-Type: multipart/alternative;
boundary="----=_NextPart_000_01B2_01C76BD0.BB7C8CE0"
X-Mailer: Microsoft Office Outlook 11
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.3790.2826
Thread-Index: Acdr8j9xbbl+S99HSxaeMhWX2Hk69g==

Ok you will notice the Message-ID: shows @windowsdomainname.com I have tried sending from another computer not on this domain and it puts in the computername, but on the windows domain it puts the name of the actual windows domain.

How can I have postfix use the domain name of the user that is trying to send? Looking at other various emails from other servers, the Message ID always shows the name of the domain of the user that is sending the email.

the second and less important problem is the part where it says Received: from daisy2 (unknown [[12.173.196.245]])
by host.mainserverdomain.com
that has two problems, for one, it uses the machine name of the client, which is not a huge deal, and I dont think my emails would get marked as spam because of that, but how can that be changed to show to users domain name or user@domainname or something similiar, the computer name isnt very good and its kind of a security hole.

but the other problem is that it has the hostname and the main server domain listed instead of the users domain. It shouldnt show the hostname of the server, it should show the domain of the user, since you could have 300 domains on a server and the server hostname is probablly not related to the other domains at all.

So how can I clean this up a little, any suggestions. I have tried to make changes in the postfix configuariton through virtualmin, but I could not notice any changes in the message headers I received.