OWA autodelete messages in SENT

Hello,

I have an Exchange 5.5 PC with OWA installed. I have enforced storage limits to mailboxes. By default when someone is sending a message using Outlook Web Access the message is stored in SENT ITEMS FOLDER.

How can I force the Exchange Serve to automatically delete the messages that are stored in SENT ITEMS FOLDER.

PS: I am having the same problem with messages that are deleted (DELETED ITEMS FOLDER).

Thanks in advance.