语法：mail(to,subject,message,headers,parameters) 举例一：
if(mail("support@fints.us", "My Subject", "Line 1\nLine 2\nLine 3"))
{ echo "Mail has been sent."; }
else
{ echo "Can not send mail."; }
?>

举例二：
mail(
"support@fints.us",
"Contact request", //邮件标题
$string, //邮件主体内容，按照手册的说法，Line行每行不能超过70个字符。
"From: info@fints.com.cn\nReply-To: xuzhaohua98@yahoo.com.cn\nContent-Type: text/html" //邮件头内容
//参数5通常省略
);