PHP 関数を使用して、電子メールの送受信用の添付ファイルをアップロードおよびダウンロードするにはどうすればよいですか?

[mail function]
SMTP = smtp.example.com
smtp_port = 25
sendmail_from = me@example.com

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

$from = 'sender@example.com';
$replyTo = 'reply@example.com';

$attachment = '/path/to/attachment.pdf';

$headers = "From: $from
";
$headers .= "Reply-To: $replyTo
";
$headers .= "MIME-Version: 1.0
";
$headers .= "Content-Type: multipart/mixed; boundary="boundary"
";

$attachmentContent = file_get_contents($attachment);
$attachmentContent = chunk_split(base64_encode($attachmentContent));

$body = "--boundary
";
$body .= "Content-Type: text/plain; charset=UTF-8

";
$body .= "$message

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

";
$body .= "$attachmentContent
";
$body .= "--boundary--";

if (mail($to, $subject, $body, $headers)) {
    echo '邮件发送成功！';
} else {
    echo '邮件发送失败！';
}

$server = '{imap.example.com:993/imap/ssl}INBOX';
$username = 'username@example.com';
$password = 'password';

$mailbox = imap_open($server, $username, $password);
$emails = imap_search($mailbox, 'ALL');

foreach($emails as $email) {
    $structure = imap_fetchstructure($mailbox, $email);

    if (isset($structure->parts)) {
        foreach ($structure->parts as $partId => $part) {
            if ($part->ifdisposition && strtolower($part->disposition) == 'attachment') {
                $attachmentName = $part->dparameters[0]->value;

                $attachmentContent = imap_fetchbody($mailbox, $email, $partId + 1);
                $attachmentContent = base64_decode($attachmentContent);

                file_put_contents($attachmentName, $attachmentContent);
            }
        }
    }
}

imap_close($mailbox);