$field_rules = array(
    'name' => 'required',
    'email' => 'required|valid_email',
    'phone' => '',
    'contact_reason' => 'required',
    'message' => 'required'
);


$error_messages = array(
    'required' => 'This field is required',
    'valid_email' => 'Please enter a valid email address'
);


$error_list = '';


$fields = $_POST;



if (!empty($fields))
{
    //Validate each of the fields
    foreach ($field_rules as $field => $rules)
    {
        $rules = explode('|', $rules);

        foreach ($rules as $rule)
        {
            $result = null;

            if (isset($fields[$field]))
            {
                if (!empty($rule))
                    $result = $rule($fields[$field]);

                if ($result === false)
                {
                    $field_name = ucwords(implode(' ', explode('_', $field)));

                    $error_list .= "<div class='error'>$field_name: " . $error_messages[$rule] . "</div>";
                }
            }
        }
    }

    if (empty($error_list))
    {
        $subject = '[Contact Form] New message from ' . $fields['name'] . '.';

        $content = $fields['name'] . " sent you a message from your contact form:rnn";
        $content .= "-------n" . $fields['message'] . "rnn";
        $content .= "Contact Reason: " . $fields['contact_reason']
                . " nnEmail: " . $fields['email']
                . " nnPhone: " . $fields['phone'] . " nn";

        if (mail($email_address, $subject, $content, "From: " . $fields['email'] . "rnReply-To: " . $fields['email'] . "rnReturn-Path: " . $fields['email'] . "rn"))
        {

            echo "<h2 class='success'>Message Sent</h2>";
            echo "<br/><p class='success'>Thank you <strong>" . $fields['name'] . "</strong>, your message has been submitted and someone will contact you shortly.</p>";
        }
        else
        {

            echo 'ERROR!';
        }
    }
}


function valid_email($str)
{
    return eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$", $str) ? false : true;
}

<?php
# Validation Class
# www.C0derz.com
# GPL License 
class Validation 
{
	public static function Is_alpha($string,$min,$max)
	{
		if(!Validation::Length($string,$min,$max)){return false;}
		else return (bool) eregi("^[a-zA-Z]+$",$string); 
	}
	public static function Length($string,$min,$max)
	{
		if(empty($min) && empty($max)) {return true;}
		if(empty($min) && !empty($max)){if(strlen($string) < $max){return true;}}
		else if(!empty($min) && empty($max)){if(strlen($string) > $min){return true;}}
		else if(strlen($string) > $min && strlen($string) < $max){return true;}else{return false;}
	}
	public static function Is_Email($string,$min,$max)
	{
		if(!Validation::Length($string,$min,$max)){return false;}
		else return (bool) filter_var($string, FILTER_VALIDATE_EMAIL);
	}
	public static function Is_Mobile($string,$min,$max)
	{
		if(!Validation::Length($string,$min,$max)){return false;}
		else return (bool) eregi("^[0-9]{8,20}$",$string);
	}	
	public static function Is_Phone($string,$min,$max)
	{
		if(!Validation::Length($string,$min,$max)){return false;}
		else return (bool) eregi("^[0-9 ]{7,13}$",$string);
	}
	public static function Is_Url($string,$min,$max)
	{
		if(!Validation::Length($string,$min,$max)){return false;}
		else return (bool) eregi("^(https?|ftp)\\:\\/\\/([a-z0-9+!*(),;?&=\$_.-]+(\\:[a-z0-9+!*(),;?&=\$_.-]+)?@)?[a-z0-9+\$_-]+(\\.[a-z0-9+\$_-]+)*(\\:[0-9]{2,5})?(\\/([a-z0-9+\$_-]\\.?)+)*\\/?(\\?[a-z+&\$_.-][a-z0-9;:@/&%=+\$_.-]*)?(#[a-z_.-][a-z0-9+\$_.-]*)?\$", $string);
	}
	public static function Is_Ip4($string)
	{
		return (bool) preg_match("/^((\d{1,2}|[01]\d{2}|2([0-4]\d|5[0-5]))\.){3}(\d{1,2}|[01]\d{2}|2([0-4]\d|5[0-5]))$/",$string);
	}
	public static function Is_Ip6($string)
	{
		if(empty($string)){return false;}
	    // fast exit for localhost
	    if (strlen($string) < 3)
	        return $string == '::';
	
	    // Check if part is in IPv4 format
	    if (strpos($string, '.'))
	    {
	        $lastcolon = strrpos($string, ':');
	        if (!($lastcolon && Validation::Is_Ip4(substr($string, $lastcolon + 1))))
	            return false;
	
	        // replace IPv4 part with dummy
	        $string = substr($string, 0, $lastcolon) . ':0:0';
	    }
	
	    // check uncompressed
	    if (strpos($string, '::') === false)
	    {
	        return preg_match('/^(?:[a-f0-9]{1,4}:){7}[a-f0-9]{1,4}$/i', $string);
	    }
	
	    // check colon-count for compressed format
	    if (substr_count($string, ':') < 8)
	    {
	        return preg_match('/^(?::|(?:[a-f0-9]{1,4}:)+):(?:(?:[a-f0-9]{1,4}:)*[a-f0-9]{1,4})?$/i', $string);
	    }
		return false;
	}
}
?>

    foreach($expected as $key) {
         
        $input = htmlspecialchars($_POST[$key]);
     
        if (array_key_exists($key, $_POST)) {
            if (empty($_POST[$key])) {
                $errors[$key] = $validation[$key];
            } else {
                if($key == 'email'){
                    if (filter_var($email, FILTER_VALIDATE_EMAIL)) {
                        $output[$key] = $_POST[$key];
                    }else{
                        $errors[$key] = 'NON VALIDATE_EMAIL'
                    }
                }else{
                   $output[$key] = $_POST[$key]; 
                }
            }
        } else {
            $errors[$key] = $validation[$key];
        }
     
    }