After migration of mailboxes, Exchange and Outlook Web Access work but iPhones/iPads are unable to communicate with the server via Outlook Anywhere protocols.
When demoting the source server using DCPROMO, the operation fails with: “The directory service was unable to transfer ownership of one or more floating single-master operation roles to other servers” (5005).
This may occur if the DNS contains name server entries referring to the source server. Remove these, run IPCONFIG /FLUSHDNS on the source server and try again.