Mine

<?php
if( isset( $_POST['submit'] ) ){
	// filter user input and store in clean array
	$clean = array();
	$clean['subject'] 	= htmlentities($_POST['subject'], 
ENTQUOTES, "UTF-8");
	$clean['name'] 		= htmlentities($_POST['name'], 
ENTQUOTES, "UTF-8");
	$clean['email'] 	= htmlentities($_POST['email'], 
ENTQUOTES, "UTF-8");
	$clean['message'] 	= htmlentities($_POST['message'], 
ENTQUOTES, "UTF-8");
	
	// check for required fields here.
	// first set $errors to an empty string. we will check its type 
later
	$errors = '';
	if( !isset($_POST['subject']) || strlen($_POST['subject'] < 1) )
	{
		$errors[] = "Please enter a subject"; 
	}
	if( !isset($_POST['name']) || strlen($_POST['name'] < 1) )
	{
		$errors[] = "Please enter your name"; 
	}
	if( !isset($_POST['email']) || strlen($_POST['email'] < 1) )
	{
		$errors[] = "Please enter your email"; 
	}
	if( !isset($_POST['message']) || strlen($_POST['message'] < 1) )
	{
		$errors[] = "Please enter a message"; 
	}
	
	// if errors is an array then we know that we have errors, if 
not, then send out email
	if( is_array($errors) )
	{
		// loop through the errors array and display them here.
	}
	else
	{
		$to 			= "etement@gmail.com";
		$subject_field	= $clean['subject'];
		$name_field 	= $clean['name'];
		$email_field 	= $clean['email'];
		$message 		= $clean['message'];
		$ip = $_SERVER["REMOTE_ADDR"]; 
		$body = "From: $name_field\n E-Mail: $email_field\n IP: 
$ip
		\n Subject: $subject_field\n Message:\n $message";
		 
		echo "Message has been sent!";
		mail($to, $subject_field, $body);
	}
} 
else{
	echo "Please enter appropriate information:";
}
?>