internal ip address

[alexbo at myself.com]

Hi there,
my Linux server has MailScanner v4.65.3 with postfix v2.1.5
When, for example, I send a message from a pc whose internal ip address is 10.0.0.175 taking a look in the headers of outgoing mail I've seen the last header just before Message-ID to appear like that

Received: from [10.0.0.175] (pc1 [10.0.0.175])
by smtp.vvv.net (Postfix) with ESMTP id 6EBF7A75C7
    for <aaa at mail.com>; Tue,  5 Feb 2008 14:16:09 +0100 (CET)

Why the ip address of the sender is shown (twice) in square brackets ?

My task is avoiding the outer world to know the internal ip of the sender... so googling on the internet I seen a similar case on

www.securityfocus.com/archive/91/421789/30/

using "Remove These Headers" rule but after doing those modifications I've noticed that all outgoing mail is marked to be received from "Unknown".
Many other searches on the net returned no results at all, so I will know if somebody could help this poor man how to hide internal ip address ot the sender avoiding last issue.

-- 
Thank you,
Alex

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