I have Exchange 2007 installed in a child domain. I have found that the ExchangeRecipient Administrators group does not have permissions on the users mailboxes. Setup /PrepareAllDomains was run on the root domain. Does anyone know what may have caused this and how to correct?Will running setup / PrepareDomain reapply these permissions and if so are there any issues if Inow run setup /PrepareDomain in a running environment?

Have you confirmed replication between root and child. Did you run all the other steps beforehand?

Everything appears OK. The Microsoft Exchange System Objects container has been created and the Exchange Install Domain Servers group has been correctly added and populated. Is there anything else I should be looking for?

OK I have found the answer. My problem was in fact that Recipient Administrators could not change permissions on a mailbox, rather than not having permissions to a mailbox. I should have read the help better. To run the Add-MailboxPermission cmdlet on a computer that has the Mailbox server role installed, you must log on be using an account that is a member of the Exchange Organization Administrators group. The account must also be a member of the local Administrators group on that computer.