If you update your Blackberry Server to 5.0.3 you might see some hangs, deadlocks and crashes. RIM/BlackBerry released a knowledge base article who explains the issue and offer a fix.
The potential hang is triggered based on a specific interaction between the BlackBerry Enterprise Server and the mail server to process unread marks for BlackBerry enabled users. During this process the BES passes over a list of NoteIDs to the mail server. If the size of this list is > 10K and the mail server interacting with the BES has transaction logging enabled, the mail server can experience a hang. Its difficult to predict if any one list would be greater than 10K of unread messages. To be conservative, any environment with larger mail files and transaction logging enabled should request this fix.
Secondary issues that may show up are deadlocks involving semaphores & server crashes. However, the primary indicator for this issue is the hang. No hang will be experienced on the BES Domino server itself.
This issue is logged as IBM SPR JPAI8E4NTW .
This issue will happen with BES Domino version 5.0.3 and above with any version of Domino mail server 6.0 and above.
Resolving the problem
Workaround: Disable read/unread mark synchronization for the BES (both active and standby if utilizing HA configuration) with the following registry key.
On the BlackBerry Enterprise Server, browse to HKEY_LOCAL_MACHINE\SOFTWARE\Research In Motion\BlackBerry Enterprise Server\Agents\. Create the DWORD value UnreadMarksDisabled.
Enter a value 1 to prevent read/unread message status functionality. Enter a value of 0 to enable this functionality.
Fix: The fix for SPR JPAI8E4NTW is in 8.5.2FP2 and 8.53. The mail servers which interact with the BES must be upgraded. The BES server does not need to be upgraded.