A PHP script to validate the contact form on contact.php and either send the user back to the contact page to fix their errors or forgotten data entry or echo a success message that their form was mailed off after they were validated and accepted for not being a spam bot.

confirmation.php

<?php
/*
 * reCaptcha spam filter is 3rd party code was provided 
 * by Google and downloaded at http://www.google.com/recaptcha/
 * 
 * Copyright (c) 2007 reCAPTCHA -- http://recaptcha.net
 * AUTHORS:
 *   Mike Crawford
 *   Ben Maurer
 * 
 */

    require_once('captcha/recaptchalib.php');
    $privatekey = "6LclzuASAAAAAGi0i3UlWLoIP0--M_IzucxfL0QT";
    $resp = recaptcha_check_answer ($privatekey,
                                $_SERVER["REMOTE_ADDR"],
                                $_POST["recaptcha_challenge_field"],
                                $_POST["recaptcha_response_field"]);

/********************************************************************************/
/*
 * Email validation code written by Jason Breitigan
 * http://www.innermindco.com
 * 
 */

    // we already have an empty array $err setup to hold errors    
    
    $name  = (isset($_POST['name'])) ? trim($_POST['name']) : null;
    $email = (isset($_POST['email'])) ? trim($_POST['email']) : null;
    $comments = (isset($_POST['comments'])) ? trim($_POST['comments']) : null;
    
    // Validate captcha
    if( ! $resp->is_valid ) $err['captcha'] = 'Captcha Invalid';

    // validate user entered a name
    if( ! $name ) $err['name'] = 'Name Required';
    
    // validate user entered an email address, and that the email address is properly formatted
    if( ! $email ) $err['email'] = 'Email Required';
    elseif ( ! filter_var($email, FILTER_VALIDATE_EMAIL) ) $err['email'] = 'Invalid Email Address Format';
    
    // validate user entered some comments
    if ( ! $comments ) $err['comments'] = 'Comments Required';
    
    
    // check if we caught any errors, if we did not catch any errors, we can call the mail function 
    if( ! $err ){
        $to = "[email protected]";
        $subject = "{$name} contacted you at foobar.com";
        $headers = "From: {$email}\r\n" ."X-Mailer: php";
        if ( ! @mail($to, $subject, $comments, $headers)){
            $err['mail'] = 'An unknown error prevented the message from being sent!';
        }
    }

?>