using [] at the end of the name means that the select list is set to be a multiple select list.
a multiple select list passes the selections as an array.
in the email message remove the [] from the binding code, and add the following code at line 1 of the page to convert the array to a comma separated list:
<?php
if($_SERVER["REQUEST_METHOD"] == "POST") {
foreach($_POST as $key => $val) {
if(is_array($_POST[$key])) $_POST[$key] = implode(", ", $_POST[$key]);
}
}
?>