What is the difference between using the "PoliteMail mail server" and "Your Outlook Outbox" in the server connection settings?

PoliteMail always works with your Exchange server and your Outlook client, however by choosing the “PoliteMail mail server” setting gives you additional features in PoliteMail, and can improve the offloading of messages from Outlook to Exchange by intervening and spooling the messages.   For the PoliteMail server to work in this mode there are additional setup steps that must be completed, pass-through permissions allocated.