如何判断一封邮件是否来自内网？

ysunbeam

邮件头如下：
Return-path: <XXX@gmail.com>
Received: from xxx.com ([X.X.X.X])
by XXX02.xxx.com (iPlanet Messaging Server 5.2 HotFix 2.14 (built Aug
8 2006)) with ESMTP id <[email=0KDB00JBU6JWCU@.xxx.com]0KDB00JBU6JWCU@.xxx.com[/email]> for
xxxxx@xxx.com; Sun, 11 Jan 2009 21:23:56 +0800 (CST)
Received: from XXXX.xxx.com ([X.X.X.X])
by XXX01-in.xxx.com (iPlanet Messaging Server 5.2 HotFix 2.14 (built Aug
8 2006)) with ESMTP id <0KDB00JBG6JW0P@szxga01-in.xxx.com> for
xxxxx@xxx.com (ORCPT xxxxx@xxx.com); Sun,
11 Jan 2009 21:23:56 +0800 (CST)
Received: from localhost (localhost [127.0.0.1])
by szxrg01-in.xxx.com (MOS 3.8.4-GA) id CEQ40435; Sun,
11 Jan 2009 21:23:56 +0800 (CST)
Received: from qb-out-1314.google.com (qb-out-1314.google.com [72.14.204.174])
by szxrg01-in.xxx.com (MOS 3.8.4-GA) with ESMTP id CEQ40431; Sun,
11 Jan 2009 21:23:55 +0800 (CST)
Received: by qb-out-1314.google.com with SMTP id d12so3944308qbc.14 for
<xxxxx@xxx.com>; Sun, 11 Jan 2009 05:23:54 -0800 (PST)
Received: by 10.142.126.6 with SMTP id y6mr6167303wfc.24.1231680233916; Sun,
11 Jan 2009 05:23:53 -0800 (PST)
Date: Sun, 11 Jan 2009 14:23:53 +0100
From: xxxxx xxxxx <XXXX@gmail.com>\

邮件头中的10.142.126.6是否就是我们局域网的IP呢？如何才能判断这个IP是否为内网的IP呢？谢谢！

ysunbeam

昨天测试了一下，好像GMAIL所发出的邮件都带一个这样子的IP，看来应该是gmail自己的内网IP