Troubleshoot pop3 bounce settings

I've setup an email campaign in 6.2. The reply address is a "info" sharedmailbox. I've set the pop3 settings to check this mailbox for bounce mails. This was not working out the way I wanted as Sitefinity empties the mailbox, including all other customer mails. So I've setup a forward to forward all mails from info to an other mailbox, so Sitefinity can empty this mailbox.
Unfortunately this doesn't work either. The POP3 check is successful but the mails are still in the mailbox. Als the send success rate is 100% but I can see bounce mails in the mailbox. 
Where can I find a log or something where I can see what is going wrong?