Send HTML email in PHP

mail.php

<?php
$e = 'bob123@somewhere.com';
$u = 'bob123';
$p = 'password123';

ob_start(); 
include('output_page.php');
$message = ob_get_contents();
ob_end_clean();

$to = "bob123@somewhere.com";  
$from = "sam444@nowhere.com";
$subject = 'Membersite Account Activation - ** ' . $u . ' **';
$message;
$headers = "From: $from\n";
$headers .= "MIME-Version: 1.0\n";
$headers .= "Content-type: text/html; charset=iso-8859-1\n";
mail($to, $subject, $message, $headers);

?>