This only affects blackberry messages.
However, we found a solution.
Here it is:
1. Checked the Outlook cache directory (C:\Documents and Settings\"service account"\Local Settings\Application Data\Microsoft\Outlook) and discovered that the two largest .zdb files belonged to the two MAPI profiles - BlackBerry Server and BlackBerry Manager. The BlackBerryServer(BES Admin).zdb file was 1,317,393 KB and the BlackBerryManager(BES Admin).zdb file was 485,601 KB, indicating a problem with the purge process.
2. We shutdown the Controller service and logged into Outlook with the BlackBerry Server profile. Demonstrated the problem by composing a new email message and clicking on the To: button to display the GAL, which was blank.
3. We shutdown Outlook and renamed the BlackBerryManager(BES Admin).zdb and BlackBerryServer(BES Admin).zdb files.
4. We logged into Outlook using each profile and allowed the new .zdb file to generate (~100 MB).
5. The BlackBerry Server profile required configuration as described in the Zimbra documentation, whereby the GAL must be added and configured as the default address book.
6. We logged into Outlook with the BlackBerry Server profile to demonstrate the problem was fixed (the To: button now displays the GAL).
7. We shutdown Outlook and restarted the Controller service, and tested sending and receiving using the Blackberry device.