This plugin is so fantastic and is something I've been waiting for for SO LONG. It really should be added as a base option in the installer.
Wanted to add a few notes about installing this plugin. Make sure you put it in a directory called 'chbox' inside the plugins folder. I was trying to call the folder something else and getting errors.
Also, if you want it enabled by default you can change this line in your main.inc.php:
// These cols are shown in the message list. Available cols are:
// subject, from, to, cc, replyto, date, size, status, flag, attachment
$rcmail_config['list_cols'] = array('chbox','subject', 'status', 'from', 'date', 'size', 'flag', 'attachment');
Big thanks to the developer for this!