php中正则表达式判断输入的是否是邮箱

<?php    header ( "Content-Type: text/html; charset=UTF-8" );    $reply = "";    if ( isset($_POST["email_address"]) )    {        $email_address = $_POST["email_address"];        $pattern = "/^([0-9A-Za-z\\-_\\.]+)@([0-9a-z]+\\.[a-z]{2,3}(\\.[a-z]{2})?)$/i";        if ( preg_match( $pattern, $email_address ) )        {            $reply = "您输入的电子邮件地址合法<br /><br />\n";            $user_name = preg_replace( $pattern ,"$1", $email_address );            $domain_name = preg_replace( $pattern ,"$2", $email_address );            $reply .= "用户名：".$user_name."<br />\n";            $reply .= "域名：".$domain_name."<br />\n\n";        }        else        {            $reply = "您输入的电子邮件地址不合法";        }    }?>