As a BES administrator we have all seen this issue time and time again with BlackBerry Enterprise Customers but I feel this needs to be covered again with what I have found on www.blackberry.com. Granted I am unsure of the actual publish date of this particular page, it only came to my attention recently due to the increasing number of customers having the Send As permission problem crop up again and it is not the usual KB Articles although it does make use of them linked from this page.
The SendAs Support Page has a great Decision Tree of actions and steps to follow in the event of this problem:
In my experience we are seeing implementations go in at customers where there is no Inheriting down of the Rights according to standard RIM Documentation, so this leaves us with explicitly forcing the changes at User Level and always having to run the SetSendAsPermission Tool published by RIM. Not to mention the pain and suffering we go through with some legitimate Administrators who at times have to follow the resolution steps from Microsoft with regards to protected accounts, creating new standard Domain Users and associating the Mailbox to the Admin User they login as.
RIM have even gone to the extent of creating a slide based video that can be viewed online, which is not to heavy in size, so should run well on slower connections.
The slide video is composed of 32 slides in total and is view only with no sound, the Slide video can be found here: How to Verify the Microsoft Exchange ‘Send As’ permission