Blackberry Send-As / Exchange Permission Cache
If it has been confirmed that the Send As permission is applied to the user’s account in Active Directory Users and Computers and they still cannot send email from their BlackBerry smartphone, then the Microsoft Exchange permission cache must be cleared before they can send email again.
Restart the Microsoft Exchange System Attendant and Microsoft Exchange Information Store. Restarting these services purges the Microsoft Exchange permission cache and Microsoft Exchange will read the current Send As permission from Microsoft Active Directory when the next the user sends an email.
Important Note : Restarting the Microsoft Exchange System Attendant and Microsoft Exchange Information Store is not recommended by Research In Motion.