We are in a hybrid environment where we have SBS2003 and Office365 hosted service. The premise hosted exchange is used only for internal communication and the hosted service mailboxes are for external communication. We are investigating to see if we can move the internal mailboxes to the external service (O365 hosted) and limit their ability to communicate only to specified domain or group. Would like to discuss this scenario as we are planning to upgrade our workstations and found out that Outlook 2013 won't work with SBS2003 Exchange server. Thanks.