使用postfix发送邮件，需要你对本身配置做些修正，另外，也需要你设置相应的DNS，否则发送邮件会容易当做垃圾邮件。
我们做几个步骤来看看收信的影响：
1 安装后不设置
2 设置hostname和domain
3 设置MX记录
4 设置SPF
以下说明的信息为了去除隐私信息，做过一些名称修改：
= 1 没有任何配置 =
Delivered-To: your-email@gmail.com
Received: by 10.114.181.20 with SMTP id d20cs1238waf;
Mon, 4 Jan 2010 17:33:21 -0800 (PST)
Received: by 10.141.90.17 with SMTP id s17mr7576023rvl.196.1262655201126;
Mon, 04 Jan 2010 17:33:21 -0800 (PST)
Return-Path:
Received: from localhost.localdomain ([219.232.1.2])
by mx.google.com with ESMTP id 20si58728702pwj.8.2010.01.04.17.33.18;
Mon, 04 Jan 2010 17:33:19 -0800 (PST)
Received-SPF: neutral (google.com: 219.232.1.2 is neither permitted nor denied by best guess record for domain of root@localhost.localdomain) client-ip=219.232.1.2;
Authentication-Results: mx.google.com; spf=neutral (google.com: 219.232.1.2 is neither permitted nor denied by best guess record for domain of root@localhost.localdomain) smtp.mail=root@localhost.localdomain
Received: by localhost.localdomain (Postfix, from userid 0)
id 7BF5120DF2C; Mon, 4 Jan 2010 21:33:09 -0500 (EST)
To: your-email@gmail.com
Subject: test in 95
Message-Id:
Date: Mon, 4 Jan 2010 21:33:09 -0500 (EST)
From: root@localhost.localdomain (root)
test
我们看到，发信人是root@localhost.localdomain，明显不对的
回复邮件也肯定收不到，我们至少需要用户能够回复，当然，除非你不想。
= 2 设置hostname和domain =
postconf -e "myhostname=chinastor.cn"
postconf -e "mydomain=mail.chinastor.cn"
postfix reload
postfix里面修改参数可以用以上的方式，检查参数
可以是 postconf myhostname
Delivered-To: your-email@gmail.com
Received: by 10.114.181.20 with SMTP id d20cs2044waf;
Mon, 4 Jan 2010 17:52:44 -0800 (PST)
Received: by 10.142.2.14 with SMTP id 14mr7796472wfb.93.1262656364099;
Mon, 04 Jan 2010 17:52:44 -0800 (PST)
Return-Path:
Received: from chinastor.cn ([219.232.1.2])
by mx.google.com with ESMTP id 4si15052142pwj.24.2010.01.04.17.52.43;
Mon, 04 Jan 2010 17:52:43 -0800 (PST)
Received-SPF: neutral (google.com: 219.232.1.2 is neither permitted nor denied by best guess record for domain of root@chinastor.cn) client-ip=219.232.1.2;
Authentication-Results: mx.google.com; spf=neutral (google.com: 219.232.1.2 is neither permitted nor denied by best guess record for domain of root@chinastor.cn) smtp.mail=root@chinastor.cn
Received: by chinastor.cn (Postfix, from userid 0)
id 9AB3420DF2F; Mon, 4 Jan 2010 21:52:34 -0500 (EST)
To: your-email@gmail.com
Subject: test after modify myhostname and mydomain
Message-Id:
Date: Mon, 4 Jan 2010 21:52:34 -0500 (EST)
From: root@chinastor.cn (root)
test
看到了吧？
发信人是 root@chinastor.cn 了，这用户至少知道是谁发的
如果用户回复邮件，那就会发到chinastor.cn指定的邮件服务器，这个是通过DNS查询判断发送到哪里的。
下面来修改DNS：
= 3 设置DNS =
添加一条MX记录：@ MX mail.chinastor.cn.
再添加一条A记录： mail A your_IP
一般建议不直接指向IP
收到的邮件无变化，忽略邮件说明。
= 4 设置SPF =
细心的话，可以看的出来，gmail有一段信息：
Received-SPF: neutral (google.com: 219.232.1.2 is neither permitted nor denied by best guess record for domain of root@chinastor.cn) client-ip=219.232.1.2;
Authentication-Results: mx.google.com; spf=neutral (google.com: 219.232.1.2 is neither permitted nor denied by best guess record for domain of root@chinastor.cn) smtp.mail=root@chinastor.cn
SPF是什么？
SPF 是发送方策略框架
(Sender Policy Framework) 的缩写，一种以IP（互联网协定）地址认证电子邮件寄件人身份的技术，是非常高效的垃圾邮件解决方案，旨在应对垃圾邮件中的一个特别问题——发送方假冒问题。当用户定义了他的域名SPF记录之后，接收邮件方会根据该用户的SPF记录来确定连接过来的IP地址是否被包含在SPF记录里面，如果在，则认为是一封正确的邮件，否则则认为是一封伪造的邮件。因此，那些发信人伪造域名的垃圾邮件在SPF的火眼金睛下再也无法隐藏，企业邮箱就可以有效地避免此类垃圾邮件。
设置SPF可以有简单的方法：
http://old.openspf.org/wizard.html
DNS添加一条TXT记录:
v=spf1 mx a:mail.chinastor.cn ~all
邮件会不一样：
Delivered-To: your-email@gmail.com
Received: by 10.114.181.20 with SMTP id d20cs2325waf;
Mon, 4 Jan 2010 17:58:31 -0800 (PST)
Received: by 10.141.100.8 with SMTP id c8mr13115112rvm.201.1262656711500;
Mon, 04 Jan 2010 17:58:31 -0800 (PST)
Return-Path:
Received: from chinastor.cn ([219.232.1.2])
by mx.google.com with ESMTP id 35si27159111pxi.23.2010.01.04.17.58.30;
Mon, 04 Jan 2010 17:58:30 -0800 (PST)
Received-SPF: pass (google.com: domain of root@chinastor.cn designates 219.232.1.2 as permitted sender) client-ip=219.232.1.2;
Authentication-Results: mx.google.com; spf=pass (google.com: domain of root@chinastor.cn designates 219.232.1.2 as permitted sender) smtp.mail=root@chinastor.cn
Received: by chinastor.cn (Postfix, from userid 0)
id 8C66C20DF2F; Mon, 4 Jan 2010 21:58:21 -0500 (EST)
To: your-email@gmail.com
Subject: test after setting SPF
Message-Id:
Date: Mon, 4 Jan 2010 21:58:21 -0500 (EST)
From: root@chinastor.cn (root)
test
也就是通过了SPF检查，这样一般的邮件服务器都不会认为你的是垃圾邮件，除非很多人举报你。
当然，能够设置PTR记录就更加完美了。