FYI：初学php时写的php邮件发送类

<?php

/**
 * 功能: 发送邮件
 * 版本: 0.1
 * 日期: 2007-6-4 18:58:50
 * 作者: willko ([e-mail], http://www.willko.cn)
 * 版权: (C)版权所有 willko
 */

class hellomail {
	private $host;
	private $port;
	private $username;
	private $password;
	private $auth;
	private $fp;
	public $cn;
/**
 * 功能 : 初始化
 * $host : SMTP地址
 * $username : SMTP用户名 (如果需要身份验证必填)
 * $password : SMTP密码 (如果需要身份验证必填)
 * $auth : SMTP服务器是否需要身份验证，true表示需要
 * $port : SMTP端口
 * 
 * @param string $host
 * @param string $username
 * @param string $password
 * @param int $port
 * @param bool $auth
 */
	public function __construct($host, $username=null, $password=null, $auth=false, $port=25) {
		$this->host = $host;
		$this->port = $port;
		$this->username = $username;
		$this->password = $password;
		$this->auth = $auth;
		$cn = getenv('COMPUTERNAME');
	}
/**
 * 功能 : 发送邮件
 * $header['from'] : 发件人 (必须)
 * $header['to'] : 收件人 (必须)
 * $header['subject'] : 主题
 * $header['reply-to'] : 回复邮箱
 * $content : 信件内容
 * 
 * @param array $headers
 * @param string $content
 */
	public function send($headers, $content=null) {
		$content = preg_replace('/<?<!\r>(\n)/', '\r\n', $content);
		$this->fp = fsockopen($this->host, $this->port, $errno, $errstr);
		if (!$this->fp) {
			throw new Exception("$errstr ($errno)");
		}
		$this->checkReply(220);
		$this->command("HELO {$this->cn}");
		$this->checkReply(250);
		if ($this->auth) {
			$this->command('AUTH LOGIN');
			$this->checkReply(334);
			$this->command(base64_encode($this->username));
			$this->checkReply(334);
			$this->command(base64_encode($this->password));
			$this->checkReply(235);
		}
		$this->command("MAIL FROM: <{$headers['from']}>");
		$this->checkReply(250);
		$this->command("RCPT to: <{$headers['to']}>");
		$this->checkReply(250);
		$this->command("DATA");
		$this->checkReply(354);
		$data = 'Date: ' . date('r') . "\r\n"
				. 'To: ' . $headers['to'] . "\r\n"
				. 'From: ' . $headers['from'] . "\r\n";
		if ($headers['reply-to']) {
			$data .= 'Reply-To: ' . $headers['reply-to'] . "\r\n";
		}
		$data .= 'Subject: ' . $headers['subject'] . "\r\n\r\n"
				. $content;
		$this->command($data, "\r\n.\r\n");
		$this->checkReply(250);
		$this->command('QUIT');
		fclose($this->fp);
	}
/**
 * 功能 : 检查STMP服务器返回的代码是否和$code一样
 * 
 * @param string/int $code
 */
	protected function checkReply($code) {
		$reply = fgets($this->fp, 128);
		if (substr($reply, 0, 3) != $code) {
			throw new Exception($reply);
		}
	}
/**
 * 功能 : 执行STMP命令
 *
 * @param string $cmd
 * @param string $end
 */
	protected function command($cmd, $end="\r\n") {
		fputs($this->fp, $cmd . $end);
	}
}