AD was set with all security groups, users and contacts into just the Users OU. I created a new Company OU with sub OUs of departments. I moved ALL users into the Company OU and subfolders. I also created a Security Groups OU and moved all the Domain Local & Global accounts.
The default Users OU was completely emptied out. I restarted Exchange and of course it didn't boot. I found through EE, moving any of the Exchange Service accounts from the default Users OU would cause this. I moved all the objects back to the original Users OU and deleted all the ones I created.
Apparently there are some objects which must remain in the default Users OU - what are these accounts?
If these accounts remain in the default users OU then it will be safe to recreated the Company OU with departments and move the daily user accounts to these OUs without causing any problems?