PHP -邮件服务器错误:无法连接到邮件服务器

我对php和html编码有点陌生，想知道为什么我有这个错误。邮件应该自动向我发送客户购买的信息;数量和金额通过电子邮件。然而，当我测试运行时，我经常遇到这个问题。

Warning: mail(): Failed to connect to mailserver at "localhost" port 25, verify your "SMTP" and "smtp_port" setting in php.ini or use ini_set() in C:'wamp'www'process.php on line 39
    $myusername=$_SESSION['username'];
    $sql="SELECT email FROM member WHERE username='$myusername'";
    $result=mysql_query($sql);
    $from = $result;
    $subject = $myusername . "'s Purchases of ". $_SESSION['amount'] ." of XXXX.";
    $message = $_SESSION["payamount"] . "via CHEQUE/Cash on Collection.";
    $mail = mail("okay1@gmail.com",$subject,$message,"From: $from'n");