Symptoms
When you try to grant the Send As permission of a linked mailbox in an account forest in Microsoft Exchange Server 2013, the permission is granted to a disabled user in the Exchange Server 2013 forest instead of the user in the account forest.
Resolution
To fix this issue, install Cumulative Update 15 for Exchange Server 2013 or a later cumulative update for Exchange Server 2013.
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about the terminology that Microsoft uses to describe software updates.
