CodeIgniter从Ubuntu服务器发送邮件

当我从本地安装（Mac OSX）发送邮件时，发送邮件没有问题。

我现在已经将我的CodeIgniter项目上传到主机Linode，在那里我安装了Ubuntu服务器。但现在我不能再发邮件了。我已经为sendmail安装了Postfix，但它一直在说：

Return-Path: <do_not_reply@XXX.com>
X-Original-To: XXX@XXX.com
Delivered-To: XXX@XXX.com
Received: by XXX.com (Postfix, from userid 33)
    id B332327FE9; Thu, 17 Dec 2015 11:41:32 +0100 (CET)
To: XXX@XXX.com
Subject: XXXXXXXXXXXXXXXXXXXXXXXXXX
X-PHP-Originating-Script: 0:Email.php
User-Agent: PHPMailer
Date: Thu, 17 Dec 2015 11:41:32 +0100
From: "XXXX" <XXX@XXX.com>
Reply-To: "XXX@XXX.com" <XXX@XXX.com>
X-Sender: XXX@XXX.com
X-Mailer: PHPMailer
X-Priority: 3 (Normal)
Message-ID: <5672915cb1605@XXX.com>
Mime-Version: 1.0
Content-Type: multipart/mixed; boundary="B_ATC_5672915cb168a"
This is a multi-part message in MIME format.
Your email application may not support this format.
--B_ATC_5672915cb168a
Content-Type: multipart/alternative; boundary="B_ALT_5672915cb164d"
--B_ALT_5672915cb164d
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

有人能帮忙吗。解释我做错了什么？发送邮件的PHP代码只是标准的。