如何使用ubuntu操作系统在PHP中发送邮件

这是我的代码，我在项目文件夹中包含了mime.php、mail.php、and Mail.php等所有文件，但邮件功能仍然不起作用。

<?php
require "Mail.php";
require_once 'Mail/mime.php';
require_once 'Mail/mail.php';
$to = "mymail@gmail.com";
$from = "sendmail@gmail.com";
$subject = utf8_decode("mail");
$message = utf8_decode("hi");
$attachment_data = utf8_decode("testingmail1-filecontent");
$attachment_filename = utf8_decode("testingmail1.php");
send_mail_utf8_with_attachment($to, $from, $subject, $message ,$attachment_data, $attachment_filename);
function send_mail_utf8_with_attachment($to, $from, $subject, $message = "",$attachment_data="", $attachment_filename="")
{
    $params = array();
    $params['head_charset'] = 'utf-8';
    $params['text_charset'] = 'utf-8';
    $params['html_charset'] = 'utf-8';
    $params['eol'] = "'n";
    $hdrs = array('From'    => $from ,'Subject' => $subject );
    $mime = new Mail_mime($params);
    $mime->setTXTBody($message);
    if (strlen($attachment_data) && strlen($attachment_filename))
    {
        $mimeType = "application/octet-stream";
        $mime->addAttachment($attachment_data, $mimeType, $attachment_filename, false);
    }
    $body = $mime->get();
    $hdrs = $mime->headers($hdrs);
    $mail =& Mail::factory('mail');
    return $mail->send($to, $hdrs, $body);
} 
?>

我已经实现了所有安装：

sudo apt-get install php-pear
sudo pear install mail
sudo pear install Net_SMTP
sudo pear install Auth_SASL
sudo pear install mail_mime

但它仍然不起作用。