如何使用PHP函数进行邮件发送和接收的邮件群发和邮件队列处理？

// 邮件发送配置
$smtp_server = 'smtp.gmail.com';
$smtp_port = 587;
$smtp_username = 'your-email@gmail.com';
$smtp_password = 'your-password';

// 邮件内容
$to = 'recipient@example.com';
$subject = '邮件主题';
$message = '邮件内容';

// 创建SMTP客户端
$smtp = new SMTPClient($smtp_server, $smtp_port);
$smtp->auth($smtp_username, $smtp_password);

// 发送邮件
$smtp->send($to, $subject, $message);

$recipients = ['user1@example.com', 'user2@example.com', 'user3@example.com'];
$subject = '邮件主题';
$message = '邮件内容';

// 创建SMTP客户端
$smtp = new SMTPClient($smtp_server, $smtp_port);
$smtp->auth($smtp_username, $smtp_password);

// 逐个发送邮件
foreach ($recipients as $recipient) {
    $smtp->send($recipient, $subject, $message);
}

// 邮件任务添加到队列中
$recipients = ['user1@example.com', 'user2@example.com', 'user3@example.com'];
$subject = '邮件主题';
$message = '邮件内容';
$mailQueue->add($recipients, $subject, $message);

// 后台任务或定时任务发送邮件
$queuedMails = $mailQueue->getQueuedMails();
foreach ($queuedMails as $queuedMail) {
    $smtp->send($queuedMail['recipient'], $queuedMail['subject'], $queuedMail['message']);
    $mailQueue->markAsSent($queuedMail['id']);
}