RPI PHP

<?php

$first_name = $_POST['first_name'];
$surname = $_POST['surname'];
$email = $_POST['email'];
$msg = $_POST['message'];
$to = "****************@gmail.com";
$subject = "Get in Touch";
mail($to, $subject, $msg, "From: " . $first_name . $surname);
echo "Your Message has been sent.";
header( 'Location: contactformsent.html' ) ;
?>