Done that, here's my original function
function sendEmail($i_email, $i_subject, $i_BookingCode, $i_CustomerName){
$to = $i_email;
$subject = $i_subject;
$headers = "From: bookings@mydomain.com\r\n";
$headers .= "Reply-To: bookings@mydomain.com\r\n";
$headers .= "MIME-Version: 1.0\r\n";
$headers .= "Content-Type: text/html; charset=ISO-8859-1\r\n";
$message = '<html><body>';
$message .= '<img style="width: 100%;" src="images/header.png">';
$message .= '<table rules="all" style="border-color: #666;" cellpadding="10">';
$message .= "<tr style='background: #eee;'><td><strong>Booking Code:</strong> </td><td>" . $i_BookingCode. "</td></tr>";
$message .= "<tr><td><strong>Customer Name:</strong> </td><td>" . $i_CustomerName . "</td></tr>";
$message .= "</table>";
$message .= "</body></html>";
mail($to, $subject, '$message', $headers) or die ('Error Sending Email.');
}