Send an email with PHP

<?php

function clean($string){
	return htmlspecialchars(strip_tags($string));
}

if (isset($_POST["send_enquiry"])) {

	$response_array = array();

	$user_name = clean($_POST["user_name"]);
	$user_company = clean($_POST["user_company"]);
	$user_email = clean($_POST["user_email"]);
	$user_message = clean($_POST["user_message"]);

	
	$to = "EMAIL";
	$subject = "SUBJECT";
	$from = "From: [email protected]";

	$message = $user_name . " would like to find out more about you .\n\nName: " . $user_name . "\nCompany: " . $user_company . "\nEmail: " . $user_email . "\nMessage: " . $user_message;
	
	mail($to,$subject,$message,$from);
	
	$response_array['status'] = 'success';
	$response_array['message'] = 'Done';

	echo json_encode($response_array);
	
	exit($encoded);
};