在PHP中调用Sendmail发送E_mail

<?
$fp = popen("/usr/sbin/sendmail 收信人的E-mail","w");
fputs($fp,"Subject: 主題/n");
fputs($fp,"From: 寄信人/n");
fputs($fp,"Reply-to: e-mail");
fputs($fp,"信件內容 /n");
fputs($fp,"./n"); //信件結尾以一個句號做結尾
pclose($fp);
?>