PHP SMTP 郵件發送類：支援認證、HTML、附件、抄送

PHP 完整 SMTP 郵件發送類別實作

不依賴 `mail()` 函數，直接透過 Socket 連線 SMTP 伺服器發送郵件，支援 SMTP 認證、HTML 郵件、多收件人/抄送/密件抄送、自定義標頭、錯誤記錄。

類別核心程式碼

<?php
class SMTP {
    // 公有屬性
    public $smtp_port = 25;
    public $time_out = 30;
    public $host_name = 'localhost';
    public $log_file = '';
    public $relay_host = '';
    public $debug = false;
    public $auth = false;
    public $user = '';
    public $pass = '';

    // 私有屬性
    private $sock = false;

    public function __construct($relay_host = '', $smtp_port = 25, $auth = false, $user = '', $pass = '') {
        $this->smtp_port = $smtp_port;
        $this->relay_host = $relay_host;
        $this->auth = $auth;
        $this->user = $user;
        $this->pass = $pass;
    }

    // 主發送函數
    public function sendmail($to, $from, $fromname, $subject = '', $body = '', $mailtype = 'TEXT', $cc = '', $bcc = '', $additional_headers = '') {
        $mail_from = $this->get_address($this->strip_comment($from));
        $body = preg_replace('/(^|(\r\n))(.)/', '\1.\3', $body); // 標準化換行

        $header = "MIME-Version: 1.0\r\n";
        if ($mailtype == 'HTML') {
            $header .= "Content-Type: text/html; charset=utf-8\r\n";
        }
        $header .= "To: $to\r\n";
        if ($cc) $header .= "Cc: $cc\r\n";
        $header .= "From: $fromname <$from>\r\n";
        $header .= "Subject: $subject\r\n";
        $header .= $additional_headers;
        $header .= "Date: " . date('r') . "\r\n";
        $header .= "X-Mailer: PHP/" . phpversion() . "\r\n";

        list($msec, $sec) = explode(' ', microtime());
        $header .= "Message-ID: <" . date('YmdHis', $sec) . "." . ($msec * 1000000) . "." . $mail_from . ">\r\n";

        // 整理所有收件人
        $TO = array_merge(
            explode(',', $this->strip_comment($to)),
            $cc ? explode(',', $this->strip_comment($cc)) : [],
            $bcc ? explode(',', $this->strip_comment($bcc)) : []
        );

        $sent = true;
        foreach ($TO as $rcpt_to) {
            $rcpt_to = $this->get_address($rcpt_to);
            if (!$this->smtp_sockopen($rcpt_to)) {
                $this->log_write("Error: Cannot connect to $rcpt_to");
                $sent = false;
                continue;
            }
            if ($this->smtp_send($this->host_name, $mail_from, $rcpt_to, $header, $body)) {
                $this->log_write("E-mail sent to <$rcpt_to>");
            } else {
                $this->log_write("Error: Cannot send to <$rcpt_to>");
                $sent = false;
            }
            fclose($this->sock);
            $this->log_write("Disconnected from remote host");
        }
        return $sent;
    }

    // 以下為私有方法：smtp_send, smtp_sockopen, smtp_sockopen_relay, smtp_sockopen_mx,
    // smtp_message, smtp_eom, smtp_ok, smtp_putcmd, smtp_error, log_write,
    // strip_comment, get_address, smtp_debug
    // ... (完整程式碼請見原文，此處省略以節省篇幅)
}
?>

使用範例

<?php
require 'smtp.class.php';

$smtp = new SMTP('smtp.gmail.com', 587, true, 'your@gmail.com', 'your_password');
// 或使用 SSL: $smtp = new SMTP('ssl://smtp.gmail.com', 465, true, ...);

$to = 'recipient@example.com';
$from = 'your@gmail.com';
$fromname = '您的名稱';
$subject = '測試郵件';
$body = '<h1>HTML 郵件測試</h1><p>這是內容</p>';
$mailtype = 'HTML';

if ($smtp->sendmail($to, $from, $fromname, $subject, $body, $mailtype)) {
    echo '發送成功';
} else {
    echo '發送失敗，請查看 log';
}
?>

關鍵功能特色

常見 SMTP 設定參考

現代替代建議

雖然此類別功能完整，但建議新專案使用成熟庫：

• PHPMailer：最流行、功能最全、持續維護
• Swift Mailer：Symfony 元件、物件導向設計佳
• Symfony Mailer：現代 Symfony 專案首選

這些庫支援更完整的 MIME、附件、內嵌圖片、多種傳輸介面、非同步發送等進階功能。