Let's keep in mind also that having a copy of sent messages in the 'sent items' folder is a client side function. It is not part the server's send message (SMTP) process. When you send a message from Outlook, Thunderbird, EMclient or the Kerio client, the client first hands the message to the server (SMTP), then the client simply makes a copy of the message in the 'Sent Items' folder This is when it bumps into the quota limit.