PHP发送邮件：如何自定义reply-to头部以及附件

function mailSend($to, $subject, $message, $attach, $from, $replyto) {
//定义边界线
$boundary = uniqid();
//生成邮件头
$header = "From: $from
Reply-to:$replyto
Content-type: multipart/mixed; boundary=\"$boundary\"";
//获取附件文件的MIME类型
$mimeType = mime_content_type($attach);
//对附件文件进行编码和切分
$fp = fopen($attach, "r");
if ($fp) {
$content = fread($fp, filesize($attach));
$content = chunk_split(base64_encode($content));
fclose($fp);
}
else {
die("Failed to open file…");
}
//生成邮件主体
$body = "
–$boundary
Content-type: text/plain; charset=utf-8;
Content-transfer-encoding: 8bit
$message
–$boundary
Content-Type: $mimeType; name=$attach
Content-Disposition: attachment; filename=$attach
Content-Transfer-Encoding: base64
$content
–$boundary–";
//发送邮件
mail($to, $subject, $body, $header) or die("Failed to send mail…");
}