It's possible that the BES is connecting to the CASArray with only one name, and the agent creation algorithm is in the default "Advanced" mode. In Exchange 2003 there would be one agent per server, and if an Agent were to become hung, then that would cause an outage for all users on that server. Conversely, in Exchange 2010, all users share the same agent and if there is a problem with that agent, then all users are affected.
Although this doesn't solve the root problem, this is how to mitigate risk, at the cost of CPU and memory load on the BES server by creating more agents
Configuring the BlackBerry Enterprise Server to use the simple user distribution algorithm enumerates the total amount of BlackBerry users and divides them evenly across Messaging Agents. When set to 1, the simple algorithm is used; when set to 2, the complex algorithm is used (complex is the out-of-box default of the BlackBerry Enterprise Server). The redistribution of users can help provide relief, as the BlackBerry Enterprise Server load can be subdivided more effectively for a Microsoft Exchange 2010 environment. In previous versions of Microsoft Exchange, the user's ServerDN was a factor in determining where the user would be placed; since the architectural changes in Microsoft Exchange 2010, all users are seen as having the same ServerDN, as the CAS does an increased amount of the Microsoft Exchange business logic.
Note: This should not be implemented in a mixed Exchange environment.
Enabling Simple Messaging Agent Distribution Algorithm
The distribution algorithm can be changed with the DWORD registry key AgentOptimizeAlgorithm located in
32 bit - HKEY_LOCAL_MACHINE\SOFTWARE\Research In Motion\BlackBerry Enterprise Server\Dispatcher.
64bit - HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Research In Motion\BlackBerry Enterprise Server\Dispatcher.
DWORD value is 1 - the simple algorithm is used.
DWORD value is 2 - the complex algorithm is used.
The Default value is 2.
If the registry key does not exist, create it.
No advanced logic is used in this process.
BlackBerry smartphone users are simply distributed evenly across the number of agents specified in the two DWORD registry keys NumAgents, and NumAgentsFullServer located in:
32bit - HKEY_LOCAL_MACHINE\SOFTWARE\Research In Motion\BlackBerry Enterprise Server\Agents.
64bit - HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Research In Motion\BlackBerry Enterprise Server\Agents.
Default value is 5, do not increase it higher than 10. Make both registry keys values match.
Restart the BlackBerry Controller Service, and the BlackBerry Dispatcher Service.
Note: If the above registry keys do not exist, they need to be created.
Note: A maximum of 2 Messaging Agents will be created if the configuration database is on Microsoft SQL Database Engine (MSDE). Move the configuration database to SQL 2005 Express using KB03112.