php mail（）返回false，但不在命令行

我一直在查看stackoverflow和许多其他网站的想法，但迄今没有任何工作，我需要更多的直接帮助。

I've been looking around on stackoverflow and many other websites for ideas, but nothing has worked so far and I need more direct help.

我有一个专门的Ubuntu服务器（9.04 jaunty）和我正在运行几个PHP网站，与apache2。我的问题是mail（）函数已停止工作。自从一段时间以来，我一直在使用PEAR邮件队列大多数电子邮件，所以我不确定邮件（）停止工作，但我仍然需要一个OpenCart设置，其他一些事情，但mail（）不管我做什么，不断返回假。即使这个简单的代码也不起作用：

I have a dedicated Ubuntu Server (9.04 jaunty) and I'm running several PHP websites there, with apache2. My problem is that the mail() function has stopped working. Since a while back I've been using PEAR Mail Queue for most emails, so I'm not sure exactly when mail() stopped working, but I still need it for an OpenCart setup, among a few other things, but mail() keeps return false no matter what I do. Even this simple code won't work:

<?php
mail('mail@example.com','test','test');
?>

所以，我一直在看php.ini中的Sendmail设置，当我在命令行中运行它时，可以正常运行，并发送电子邮件：

So, I've been looking at the Sendmail-settings in php.ini which all check out, and when I run this in the command line, it works fine and sends me an email:

# sendmail
mail@example.com
test message

所以我以为可能是php本身有一个问题，所以我尝试以下命令：

So I thought it might be php itself that has a problem, so I try the following command:

# php -r "mail('mail@example.com','test','test');"

它也发送电子邮件没有任何问题！那怎么可能呢？我开始认为这可能是某种权限问题，也许www数据在运行脚本时有一些问题。仍然不确定，因为我甚至不能运行这个脚本：

And it also sends the email without any problems! So what could it be? I started thinking it might be some sort of permission problem, that maybe www-data had some issues with running the script. Still not sure about this, because I can't even run this script:

<?php
echo exec('whoami');
?>

它也返回false！我已经运行 visudo 命令，并添加以下行，以防万一：

It also returns false! I've run the visudo command and added the following line just in case:

www-data ALL=(ALL) ALL

我已将文件的用户和组所有者从 root：root 到 www-data：www-data ，但仍然没有！

And I've changed the user and group owners of the files from root:root to www-data:www-data but still nothing!

我还可以尝试什么？一定有的！任何人都可以帮助我吗？

What else can I try? There must be someting! Can anyone help me?