php中的安全性和mail()函数

我正在使用mail()发送简单的邮件.为方便起见,我使用标题来设置“发件人”地址.我想知道,我可以把那里的任何一个地址都假装成任何人;我只是为了好奇而努力,实际上它有效！这是正常的吗？这是使用邮件功能的正确方法吗？有没有办法识别这些邮件的发件人的身份？

编辑：
我使用我的Gmail地址作为邮件()标题中的“发件人”向我自己发送了一封邮件.我收到了带有这些标题的消息：

…

Received: from smarty.dreamhost.com (smarty.dreamhost.com [208.113.175.8]) by mx.google.com with ESMTP id w21si2197938ybh.68.2010.10.19.19.33.30; Tue,19 Oct 2010 19:33:30 -0700 (PDT)

Received: from nationals.dreamhost.com (nationals.dreamhost.com [69.163.165.6]) by smarty.dreamhost.com (Postfix) with ESMTP id EB56D6E804A for <myMail@gmail.com>; Tue,19 Oct 2010 19:33:29 -0700 (PDT)

Received: by nationals.dreamhost.com (Postfix,from userid 3598506) id E4BB635C83F; Tue,19 Oct 2010 19:33:29 -0700 (PDT)

Return-Path: <mySite@nationals.dreamhost.com>

Received-Spf: pass (google.com: domain of mySite@nationals.dreamhost.com designates 208.113.175.8 as permitted sender) client-ip=208.113.175.8;

Authentication-Results: mx.google.com; spf=pass (google.com: domain of mySite@nationals.dreamhost.com designates 208.113.175.8 as permitted sender) smtp.mail=mySite@nationals.dreamhost.com

发生了什么？我无法解释标题,但看起来谷歌接受了假地址！