虽然有现成的类库（如pear）可以很方便地实现附件添加和发送，但是对于一些小站点（服务器硬件、网站规模都不理想），安装pear可能会带来不必要的负担，降低web程序运行效率。
通过对邮件格式的认识，我们可以写一个脚本来发送附件。代码并不长：
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function mailsend($to, $subject, $message, $attach, $from, $replyto) {//定义边界线$boundary = uniqid();//生成邮件头$header = "from: $fromreply-to:$replytocontent-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$body = "–$boundarycontent-type: text/plain; charset=utf-8;content-transfer-encoding: 8bit$message–$boundarycontent-type: $mimetype; name=$attachcontent-disposition: attachment; filename=$attachcontent-transfer-encoding: base64$content–$boundary–";//发送邮件mail($to, $subject, $body, $header) or die("failed to send mail…");}
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以上就是php发送邮件：如何自定义reply-to头部以及附件的详细内容。