Got it working but we had to go in with ADSI Editor to delete the Database of the defunct EX16
I also needed to:
- Delete all the system and federation mailboxes (incl. those of the EX10 i guess)
- Reset the systems in AD
- Rename and give the server the exact IP address as the defunct one
- Delete all the old entries in DNS
- Rejoin AD
- Install all the Ex 16 prequisits and supportfiles (Updates, Net 4.8, UCMA?, C++ Redist., etc)
- Run PrepareAd without the /RecoverServer toggle
- Install Exchange 2016 ....
Now its at the same state before the "desaster" and of course i installed a backup sollution right after the server was joined to the AD :/
Live and Learn
Thx BR0KK