//you can do this for users instead of posts aswell
// manage_users_columns VS manage_posts_columns
add_filter('manage_posts_columns', 'column_order');
function column_order($columns) {
$n_columns = array();
$before = 'date'; // move before this (it will be the last one in the column to the far right)
foreach($columns as $key => $value) {
if ($key==$before){
$n_columns['email_id'] = 'Email To';
$n_columns['email_to'] = 'Email From';
$n_columns['email_from'] = 'Email ID';
}
$n_columns[$key] = $value;
}
return $n_columns;
}