Search for System Management.
Search for Microsoft Exchange Active Directory Topology service, right-click and choose Restart.
Then you get the calls for all connected services to also re-boot them, select yes.
Then you have to restart the Microsoft Exchange Information Store.
Here you get the question if the associated services (BlackBerry) must be restarted.
After you restarted Outlook (at account level).
If the problem is not solved, you go through all the steps again till the exchange works (sometimes up to 3 times on a slow working server).
If the problem persists, than it's advisable to restart the server and if necessary start all these services. The exchange services mostly starting automatically if you restart the server.