I have a client that has a MS Windows 2003 SBS server and we are looking to switch them to use exchange on the server, off of their current pop3 mail host. However I am not familiar with how the licensing works on SBS. Do I need to purchase Exchange licenses? They currently have 15 CAL licenses and I don't show any exchange licenses. Do we need to purchase exchange licenses under SBS or does it fall under the CAL aspect?