I have 84 users that are using Office 365. I manually created and licensed these accounts. I also have an in-house Exchange 2007 server. Management wants to migrate our e-mail to Exchange on-line. Of course I'll need to implement AD directory sync tool which will replicate our AD user accounts as mail enabled users in the Windows Azure AD. My concern is, will implementing AD sync somehow overwrite the existing accounts, possibly breaking Office 365. The ideal effect of AD sync is that it would recognize the previously created accounts and simply mail enable them. Does anyone have any insight into this?