Consider the following scenario:
You create a user account that does not have a mailbox in a Microsoft Exchange Server 2010 environment.
You configure the user account to have full access permissions for a shared mailbox.
The user logs on to the shared mailbox by using the Premium interface of Microsoft Outlook Web App (OWA Premium).
The user tries to delete an item that is in the shared mailbox.
In this scenario, the user receives the following error message:
The Mailbox you are trying to access isn't currently available. Please try again in a few minutes.
This issue occurs because OWA Premium requires the user to have a mailbox when OWA Premium tries to create the security context. If the user does not have a mailbox, a UserHasNoMailboxException exception is thrown.
To resolve this issue, install the following update rollup:
2529939 Description of Update Rollup 3 for Exchange Server 2010 Service Pack 1
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.