I am sending a test campaign to my own address and to a fictitious nonsense address and I am receiving the email at my account but I am not receiving any bounces. My settings in the config.php file are:

$message_envelope = '[email protected]';

$bounce_protocol = 'pop';
$bounce_mailbox_host = 'localhost';
$bounce_mailbox_user = '[email protected]';
$bounce_mailbox_password = 'XXXXXX';

What's the next step in figuring out the problem? I also tried both variations of the following:

$bounce_mailbox_port = "110/pop3/notls";
#$bounce_mailbox_port = "110/pop3";

I am running a Godaddy Centos 6 VPS and Plesk 11.