In a resource forest scenario you assign full access to a shared mailbox using:
Add-MailboxPermission -Identity SharedMailbox -User AccountForestDomain\UserID -AccessRights FullAccess
This provides the user in the account forest full access, but it will NOT auto-map the shared mailbox in Outlook.
If you use the command:
Add-MailboxPermission -Identity SharedMailbox -User UserID -AccessRights FullAccess
and UserID is the disabled account of the linked mailbox in the resource forest then the user in the account forest does not have the necessary permission to open the mailbox, but the auto-mapping of the mailbox in Outlook works.
You have to use both commands to have the auto-mapping feature and have access to the shared mailbox.
This looks like another issue of the auto-mapping feature. The intention of the feature is good, but the way it was implemented can be improved.
How do you configure full access to shared mailboxes in a resource forest scenario?