如何使用PHP函数进行邮件发送和接收的附件处理？

$to = 'recipient@example.com';
$subject = '邮件主题';
$message = '这是一封带有附件的邮件';

$file = '/path/to/file.pdf';  // 附件的文件路径
$filename = 'file.pdf';  // 附件的文件名

$attachment = chunk_split(base64_encode(file_get_contents($file))); // 使用base64编码附件

$boundary = md5(time());  // 设置分隔符

$headers = "From: sender@example.com
";
$headers .= "MIME-Version: 1.0
";
$headers .= "Content-Type: multipart/mixed; boundary="{$boundary}"
";

$body = "--{$boundary}
";
$body .= "Content-Type: text/plain; charset="utf-8"
";
$body .= "Content-Transfer-Encoding: 7bit

";
$body .= $message . "

";

$body .= "--{$boundary}
";
$body .= "Content-Type: application/pdf; name="{$filename}"
";
$body .= "Content-Disposition: attachment; filename="{$filename}"
";
$body .= "Content-Transfer-Encoding: base64

";
$body .= $attachment . "

";

$body .= "--{$boundary}--
";

mail($to, $subject, $body, $headers);

$hostname = '{mail.example.com:143/imap}INBOX';
$username = 'username';
$password = 'password';

$mailbox = imap_open($hostname, $username, $password) or die('无法连接到邮箱');

$mails = imap_search($mailbox, 'SUBJECT "邮件主题"');

if ($mails) {
    foreach ($mails as $mail_id) {
        $structure = imap_fetchstructure($mailbox, $mail_id);

        for ($i = 0; $i < count($structure->parts); $i++) {
            if ($structure->parts[$i]->ifdparameters) {
                foreach ($structure->parts[$i]->dparameters as $object) {
                    if (strtolower($object->attribute) == 'filename') {
                        $filename = $object->value;

                        $file_data = imap_fetchbody($mailbox, $mail_id, $i + 1);

                        // 处理附件内容...
                    }
                }
            }
        }
    }
}

imap_close($mailbox);