Recently, our parent company decided in their infinite wisdom, to absorb all of our user accounts into a single domain. The end result was a Forest/Domain where all user accounts reside, which has a forest level trust with our old forest, which is used as a resource domain for Exchange and SharePoint. User Accounts = parent.com Mailboxes = absorbed.com The migration went successfully. All user objects within absorbed.com are disabled, and the mailboxes were granted permissions through the use of linked accounts on parent.com. However, room delegation seems to be broken, since all the service accounts and rooms remained behind on the resource domain. Using Set-MailboxCalendarSettings, I can add ResourceDelegates from the resource domain (disabled accounts), but my users aren't able to accept/reject requests. Is there a way to add user accounts from parent.com as ResourceDelegates? I've been unsuccessful so far.

Hi Keeope, Based on my research, it is by design that there is no a way to add delegate across forest for resource in the scenario you described. When we add a delegate we are stamping the SID of the delegate on the mailbox who's acct is in Resource Forest (absorbed.com). When we try to accept or deny a meeting request for a resource mailbox as a delegate, the delegate account in resource forest (the lined mailbox in absorbed.com) is required for authentication. However, the authentication was not being passed to the Information Store by Outlook correctly. This is because the Outlook application and general Windows environment was running within the security confines of the account forest (parent.com), and Outlook is not designed to request credentials when we try to access a resource mailbox in absorbed.com. In order to fully support this scenario users would need to log into Windows using their resource forest credentials (absorbed.com), or migrate their mailboxes and all resource mailboxes to the new forest (parent.com). Your understanding would be appreciated. Fiona