Sometimes when you are hosting a BES server in an environment where you are hosting multiple domain names on a single BES server you need the ability to separate global address list lookups. You wouldn’t want people in one organization looking up contacts from another organization.
There is a way to do this but it involves some registry hacking:
Check to see that the users are members of the same company in Active Directory. Then in the registry go to the HKEY_LOCAL_MACHINE\Software\Research In Motion\BlackBerry Enterprise Server\Agents registry key. Create a new DWORD value called “Hosted Server”. Then in the value type in a “0″ and click ok. Then set the DWORD value for AllowAddressLookup to “0″ as well. That’s it!