Why Secondary domain sending mail from primary domain?

[sadiq007]

Hi,
My default domain(domain1.com) is working fine for both sending and receiving. Now i just added secondary domain domain2.com from admin GUI.

Now if i send mail from secondary domain (domain2.com) to anyone then the header showing domain1.com instead of domain2.com in 'Received: from' , why this?

what can i do so that mail from domain2.com have domain2.com in 'Received: from' header ?
Also there are 3 'Received: from' entries in my header , how can i read them

Below is my header.
Return-Path: <user1@domain2.com>
Received: from mail.domain1.com (mail.domain1.com [203.77.192.112])
by mx.google.com with ESMTP id u4si6828427wak.83.2010.07.26.00.26.08;
Mon, 26 Jul 2010 00:26:08 -0700 (PDT)
Received-SPF: pass (google.com: domain of user1@domain2.com designates 203.77.192.112 as permitted sender) client-ip=203.77.192.112;
Authentication-Results: mx.google.com; spf=pass (google.com: domain of user1@domain2.com designates 203.77.192.112 as permitted sender) smtp.mail=user1@domain2.com
Received: from localhost (localhost.localdomain [127.0.0.1])
by mail.domain1.com (Postfix) with ESMTP id D5F271679BFC
for <user1@gmail.com>; Mon, 26 Jul 2010 12:59:40 +0530 (IST)
X-Virus-Scanned: amavisd-new at domain1.com
Received: from mail.domain1.com ([127.0.0.1])
by localhost (mail.domain1.com [127.0.0.1]) (amavisd-new, port 10024)
with ESMTP id o-Q+rNMpkr8B for <user1@gmail.com>;
Mon, 26 Jul 2010 12:59:40 +0530 (IST)
Received: from mail.domain1.com (mail.domain1.com [192.168.0.200])
by mail.domain1.com (Postfix) with ESMTP id 5A2341679BF6
for <user1@gmail.com>; Mon, 26 Jul 2010 12:59:40 +0530 (IST)
Date: Mon, 26 Jul 2010 12:59:40 +0530 (IST)
From: user1@domain2.com
To: user1@gmail.com

Based on above header if someone want to block my domain2.com then how and which 'Received: from' address he will block?

[uxbod]

The SMTP header will always show the primary domain of the sending Zimbra server as the IP address will resolve to that by the rDNS entry.

[sadiq007]

Thanx Ux,
As my primary domain is our regulaer mailing domain(domain1.com) and i just added secodnary domain (domain2.com) for bulk-mailing , so as per you mail from both primary and secondary domain will always show primary domain in SMTP header but receiving mail-server will resove my domians Ip address using reverse DNS... so if mail from domain1.com then it will resolve IP address from its MX record mail.domain1.com and mail from domain2.com then it will resolve IP address from its MX record mail.domain2.com, so in that case if something like spamming etc done from my domain2.com mail id then only IP address of its MX record mail.domain2.com will be blocked by receiving Mail server even the SMTP header showing mail received from domain1.com .
AM I RIGHT ? plz correct me